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linux-7.2.3/Documentation/hid/amd-sfh-hid.rst
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.. SPDX-License-Identifier: GPL-2.0
AMD Sensor Fusion Hub
=====================
AMD Sensor Fusion Hub (SFH) is part of an SOC starting from Ryzen-based platforms.
The solution is working well on several OEM products. AMD SFH uses HID over PCIe bus.
In terms of architecture it resembles ISH, however the major difference is all
the HID reports are generated as part of the kernel driver.
Block Diagram
-------------
::
---------------------------------
| HID User Space Applications |
- -------------------------------
---------------------------------------------
---------------------------------
| HID Core |
---------------------------------
---------------------------------
| AMD HID Transport |
---------------------------------
--------------------------------
| AMD HID Client |
| with HID Report Generator|
--------------------------------
--------------------------------
| AMD MP2 PCIe Driver |
--------------------------------
OS
---------------------------------------------
Hardware + Firmware
--------------------------------
| SFH MP2 Processor |
--------------------------------
AMD HID Transport Layer
-----------------------
AMD SFH transport is also implemented as a bus. Each client application executing in the AMD MP2 is
registered as a device on this bus. Here, MP2 is an ARM core connected to x86 for processing
sensor data. The layer, which binds each device (AMD SFH HID driver) identifies the device type and
registers with the HID core. Transport layer attaches a constant "struct hid_ll_driver" object with
each device. Once a device is registered with HID core, the callbacks provided via this struct are
used by HID core to communicate with the device. AMD HID Transport layer implements the synchronous calls.
AMD HID Client Layer
--------------------
This layer is responsible to implement HID requests and descriptors. As firmware is OS agnostic, HID
client layer fills the HID request structure and descriptors. HID client layer is complex as it is
interface between MP2 PCIe layer and HID. HID client layer initializes the MP2 PCIe layer and holds
the instance of MP2 layer. It identifies the number of sensors connected using MP2-PCIe layer. Based
on that allocates the DRAM address for each and every sensor and passes it to MP2-PCIe driver. On
enumeration of each sensor, client layer fills the HID Descriptor structure and HID input report
structure. HID Feature report structure is optional. The report descriptor structure varies from
sensor to sensor.
AMD MP2 PCIe layer
------------------
MP2 PCIe Layer is responsible for making all transactions with the firmware over PCIe.
The connection establishment between firmware and PCIe happens here.
The communication between X86 and MP2 is split into three parts.
1. Command transfer via the C2P mailbox registers.
2. Data transfer via DRAM.
3. Supported sensor info via P2C registers.
Commands are sent to MP2 using C2P Mailbox registers. Writing into C2P Message registers generates
interrupt to MP2. The client layer allocates the physical memory and the same is sent to MP2 via
the PCI layer. MP2 firmware writes the command output to the access DRAM memory which the client
layer has allocated. Firmware always writes minimum of 32 bytes into DRAM. So as a protocol driver
shall allocate minimum of 32 bytes DRAM space.
Enumeration and Probing flow
----------------------------
::
HID AMD AMD AMD -PCIe MP2
Core Transport Client layer layer FW
| | | | |
| | | on Boot Driver Loaded |
| | | | |
| | | MP2-PCIe Int |
| | | | |
| | |---Get Number of sensors-> | |
| | | Read P2C |
| | | Register |
| | | | |
| | | Loop(for No of Sensors) | |
| | |----------------------| | |
| | | Create HID Descriptor| | |
| | | Create Input report | | |
| | | Descriptor Map | | |
| | | the MP2 FW Index to | | |
| | | HID Index | | |
| | | Allocate the DRAM | Enable |
| | | address | Sensors |
| | |----------------------| | |
| | HID transport| | Enable |
| |<--Probe------| |---Sensor CMD--> |
| | Create the | | |
| | HID device | | |
| | (MFD) | | |
| | by Populating| | |
| | the HID | | |
| | ll_driver | | |
| HID | | | |
| add | | | |
|Device | | | |
|<------------- | | | |
Data Flow from Application to the AMD SFH Driver
------------------------------------------------
::
| | | | |
| | | | |
| | | | |
| | | | |
| | | | |
|HID_req | | | |
|get_report | | | |
|------------->| | | |
| | HID_get_input| | |
| | report | | |
| |------------->|------------------------| | |
| | | Read the DRAM data for| | |
| | | requested sensor and | | |
| | | create the HID input | | |
| | | report | | |
| | |------------------------| | |
| |Data received | | |
| | in HID report| | |
To |<-------------|<-------------| | |
Applications| | | | |
<-------| | | | |
linux-7.2.3/Documentation/hid/hid-alps.rst
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==========================
ALPS HID Touchpad Protocol
==========================
Introduction
------------
Currently ALPS HID driver supports U1 Touchpad device.
U1 device basic information.
========== ======
Vendor ID 0x044E
Product ID 0x120B
Version ID 0x0121
========== ======
HID Descriptor
--------------
======= ==================== ===== =======================================
Byte Field Value Notes
======= ==================== ===== =======================================
0 wHIDDescLength 001E Length of HID Descriptor : 30 bytes
2 bcdVersion 0100 Compliant with Version 1.00
4 wReportDescLength 00B2 Report Descriptor is 178 Bytes (0x00B2)
6 wReportDescRegister 0002 Identifier to read Report Descriptor
8 wInputRegister 0003 Identifier to read Input Report
10 wMaxInputLength 0053 Input Report is 80 Bytes + 2
12 wOutputRegister 0000 Identifier to read Output Report
14 wMaxOutputLength 0000 No Output Reports
16 wCommandRegister 0005 Identifier for Command Register
18 wDataRegister 0006 Identifier for Data Register
20 wVendorID 044E Vendor ID 0x044E
22 wProductID 120B Product ID 0x120B
24 wVersionID 0121 Version 01.21
26 RESERVED 0000 RESERVED
======= ==================== ===== =======================================
Report ID
---------
========== ================= =========================================
ReportID-1 (Input Reports) (HIDUsage-Mouse) for TP&SP
ReportID-2 (Input Reports) (HIDUsage-keyboard) for TP
ReportID-3 (Input Reports) (Vendor Usage: Max 10 finger data) for TP
ReportID-4 (Input Reports) (Vendor Usage: ON bit data) for GP
ReportID-5 (Feature Reports) Feature Reports
ReportID-6 (Input Reports) (Vendor Usage: StickPointer data) for SP
ReportID-7 (Feature Reports) Flash update (Bootloader)
========== ================= =========================================
Data pattern
------------
===== ========== ===== =================
Case1 ReportID_1 TP/SP Relative/Relative
Case2 ReportID_3 TP Absolute
ReportID_6 SP Absolute
===== ========== ===== =================
Command Read/Write
------------------
To read/write to RAM, need to send a command to the device.
The command format is as below.
DataByte(SET_REPORT)
~~~~~~~~~~~~~~~~~~~~
===== ======================
Byte1 Command Byte
Byte2 Address - Byte 0 (LSB)
Byte3 Address - Byte 1
Byte4 Address - Byte 2
Byte5 Address - Byte 3 (MSB)
Byte6 Value Byte
Byte7 Checksum
===== ======================
Command Byte is read=0xD1/write=0xD2.
Address is read/write RAM address.
Value Byte is writing data when you send the write commands.
When you read RAM, there is no meaning.
DataByte(GET_REPORT)
~~~~~~~~~~~~~~~~~~~~
===== ======================
Byte1 Response Byte
Byte2 Address - Byte 0 (LSB)
Byte3 Address - Byte 1
Byte4 Address - Byte 2
Byte5 Address - Byte 3 (MSB)
Byte6 Value Byte
Byte7 Checksum
===== ======================
Read value is stored in Value Byte.
Packet Format
-------------
Touchpad data byte
~~~~~~~~~~~~~~~~~~
======= ======= ======= ======= ======= ======= ======= ======= =====
- b7 b6 b5 b4 b3 b2 b1 b0
======= ======= ======= ======= ======= ======= ======= ======= =====
1 0 0 SW6 SW5 SW4 SW3 SW2 SW1
2 0 0 0 Fcv Fn3 Fn2 Fn1 Fn0
3 Xa0_7 Xa0_6 Xa0_5 Xa0_4 Xa0_3 Xa0_2 Xa0_1 Xa0_0
4 Xa0_15 Xa0_14 Xa0_13 Xa0_12 Xa0_11 Xa0_10 Xa0_9 Xa0_8
5 Ya0_7 Ya0_6 Ya0_5 Ya0_4 Ya0_3 Ya0_2 Ya0_1 Ya0_0
6 Ya0_15 Ya0_14 Ya0_13 Ya0_12 Ya0_11 Ya0_10 Ya0_9 Ya0_8
7 LFB0 Zs0_6 Zs0_5 Zs0_4 Zs0_3 Zs0_2 Zs0_1 Zs0_0
8 Xa1_7 Xa1_6 Xa1_5 Xa1_4 Xa1_3 Xa1_2 Xa1_1 Xa1_0
9 Xa1_15 Xa1_14 Xa1_13 Xa1_12 Xa1_11 Xa1_10 Xa1_9 Xa1_8
10 Ya1_7 Ya1_6 Ya1_5 Ya1_4 Ya1_3 Ya1_2 Ya1_1 Ya1_0
11 Ya1_15 Ya1_14 Ya1_13 Ya1_12 Ya1_11 Ya1_10 Ya1_9 Ya1_8
12 LFB1 Zs1_6 Zs1_5 Zs1_4 Zs1_3 Zs1_2 Zs1_1 Zs1_0
13 Xa2_7 Xa2_6 Xa2_5 Xa2_4 Xa2_3 Xa2_2 Xa2_1 Xa2_0
14 Xa2_15 Xa2_14 Xa2_13 Xa2_12 Xa2_11 Xa2_10 Xa2_9 Xa2_8
15 Ya2_7 Ya2_6 Ya2_5 Ya2_4 Ya2_3 Ya2_2 Ya2_1 Ya2_0
16 Ya2_15 Ya2_14 Ya2_13 Ya2_12 Ya2_11 Ya2_10 Ya2_9 Ya2_8
17 LFB2 Zs2_6 Zs2_5 Zs2_4 Zs2_3 Zs2_2 Zs2_1 Zs2_0
18 Xa3_7 Xa3_6 Xa3_5 Xa3_4 Xa3_3 Xa3_2 Xa3_1 Xa3_0
19 Xa3_15 Xa3_14 Xa3_13 Xa3_12 Xa3_11 Xa3_10 Xa3_9 Xa3_8
20 Ya3_7 Ya3_6 Ya3_5 Ya3_4 Ya3_3 Ya3_2 Ya3_1 Ya3_0
21 Ya3_15 Ya3_14 Ya3_13 Ya3_12 Ya3_11 Ya3_10 Ya3_9 Ya3_8
22 LFB3 Zs3_6 Zs3_5 Zs3_4 Zs3_3 Zs3_2 Zs3_1 Zs3_0
23 Xa4_7 Xa4_6 Xa4_5 Xa4_4 Xa4_3 Xa4_2 Xa4_1 Xa4_0
24 Xa4_15 Xa4_14 Xa4_13 Xa4_12 Xa4_11 Xa4_10 Xa4_9 Xa4_8
25 Ya4_7 Ya4_6 Ya4_5 Ya4_4 Ya4_3 Ya4_2 Ya4_1 Ya4_0
26 Ya4_15 Ya4_14 Ya4_13 Ya4_12 Ya4_11 Ya4_10 Ya4_9 Ya4_8
27 LFB4 Zs4_6 Zs4_5 Zs4_4 Zs4_3 Zs4_2 Zs4_1 Zs4_0
======= ======= ======= ======= ======= ======= ======= ======= =====
SW1-SW6:
SW ON/OFF status
Xan_15-0(16bit):
X Absolute data of the "n"th finger
Yan_15-0(16bit):
Y Absolute data of the "n"th finger
Zsn_6-0(7bit):
Operation area of the "n"th finger
StickPointer data byte
~~~~~~~~~~~~~~~~~~~~~~
======= ======= ======= ======= ======= ======= ======= ======= =====
- b7 b6 b5 b4 b3 b2 b1 b0
======= ======= ======= ======= ======= ======= ======= ======= =====
Byte1 1 1 1 0 1 SW3 SW2 SW1
Byte2 X7 X6 X5 X4 X3 X2 X1 X0
Byte3 X15 X14 X13 X12 X11 X10 X9 X8
Byte4 Y7 Y6 Y5 Y4 Y3 Y2 Y1 Y0
Byte5 Y15 Y14 Y13 Y12 Y11 Y10 Y9 Y8
Byte6 Z7 Z6 Z5 Z4 Z3 Z2 Z1 Z0
Byte7 T&P Z14 Z13 Z12 Z11 Z10 Z9 Z8
======= ======= ======= ======= ======= ======= ======= ======= =====
SW1-SW3:
SW ON/OFF status
Xn_15-0(16bit):
X Absolute data
Yn_15-0(16bit):
Y Absolute data
Zn_14-0(15bit):
Z
linux-7.2.3/Documentation/hid/hid-bpf.rst
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.. SPDX-License-Identifier: GPL-2.0
=======
HID-BPF
=======
HID is a standard protocol for input devices but some devices may require
custom tweaks, traditionally done with a kernel driver fix. Using the eBPF
capabilities instead speeds up development and adds new capabilities to the
existing HID interfaces.
.. contents::
:local:
:depth: 2
When (and why) to use HID-BPF
=============================
There are several use cases when using HID-BPF is better
than standard kernel driver fix:
Dead zone of a joystick
-----------------------
Assuming you have a joystick that is getting older, it is common to see it
wobbling around its neutral point. This is usually filtered at the application
level by adding a *dead zone* for this specific axis.
With HID-BPF, we can apply this filtering in the kernel directly so userspace
does not get woken up when nothing else is happening on the input controller.
Of course, given that this dead zone is specific to an individual device, we
can not create a generic fix for all of the same joysticks. Adding a custom
kernel API for this (e.g. by adding a sysfs entry) does not guarantee this new
kernel API will be broadly adopted and maintained.
HID-BPF allows the userspace program to load the program itself, ensuring we
only load the custom API when we have a user.
Simple fixup of report descriptor
---------------------------------
In the HID tree, half of the drivers only fix one key or one byte
in the report descriptor. These fixes all require a kernel patch and the
subsequent shepherding into a release, a long and painful process for users.
We can reduce this burden by providing an eBPF program instead. Once such a
program has been verified by the user, we can embed the source code into the
kernel tree and ship the eBPF program and load it directly instead of loading
a specific kernel module for it.
Note: distribution of eBPF programs and their inclusion in the kernel is not
yet fully implemented
Add a new feature that requires a new kernel API
------------------------------------------------
An example for such a feature are the Universal Stylus Interface (USI) pens.
Basically, USI pens require a new kernel API because there are new
channels of communication that our HID and input stack do not support.
Instead of using hidraw or creating new sysfs entries or ioctls, we can rely
on eBPF to have the kernel API controlled by the consumer and to not
impact the performances by waking up userspace every time there is an
event.
Morph a device into something else and control that from userspace
------------------------------------------------------------------
The kernel has a relatively static mapping of HID items to evdev bits.
It cannot decide to dynamically transform a given device into something else
as it does not have the required context and any such transformation cannot be
undone (or even discovered) by userspace.
However, some devices are useless with that static way of defining devices. For
example, the Microsoft Surface Dial is a pushbutton with haptic feedback that
is barely usable as of today.
With eBPF, userspace can morph that device into a mouse, and convert the dial
events into wheel events. Also, the userspace program can set/unset the haptic
feedback depending on the context. For example, if a menu is visible on the
screen we likely need to have a haptic click every 15 degrees. But when
scrolling in a web page the user experience is better when the device emits
events at the highest resolution.
Firewall
--------
What if we want to prevent other users to access a specific feature of a
device? (think a possibly broken firmware update entry point)
With eBPF, we can intercept any HID command emitted to the device and
validate it or not.
This also allows to sync the state between the userspace and the
kernel/bpf program because we can intercept any incoming command.
Tracing
-------
The last usage is tracing events and all the fun we can do we BPF to summarize
and analyze events.
Right now, tracing relies on hidraw. It works well except for a couple
of issues:
1. if the driver doesn't export a hidraw node, we can't trace anything
(eBPF will be a "god-mode" there, so this may raise some eyebrows)
2. hidraw doesn't catch other processes' requests to the device, which
means that we have cases where we need to add printks to the kernel
to understand what is happening.
High-level view of HID-BPF
==========================
The main idea behind HID-BPF is that it works at an array of bytes level.
Thus, all of the parsing of the HID report and the HID report descriptor
must be implemented in the userspace component that loads the eBPF
program.
For example, in the dead zone joystick from above, knowing which fields
in the data stream needs to be set to ``0`` needs to be computed by userspace.
A corollary of this is that HID-BPF doesn't know about the other subsystems
available in the kernel. *You can not directly emit input event through the
input API from eBPF*.
When a BPF program needs to emit input events, it needs to talk with the HID
protocol, and rely on the HID kernel processing to translate the HID data into
input events.
In-tree HID-BPF programs and ``udev-hid-bpf``
=============================================
Official device fixes are shipped in the kernel tree as source in the
``drivers/hid/bpf/progs`` directory. This allows to add selftests to them in
``tools/testing/selftests/hid``.
However, the compilation of these objects is not part of a regular kernel compilation
given that they need an external tool to be loaded. This tool is currently
`udev-hid-bpf <https://libevdev.pages.freedesktop.org/udev-hid-bpf/index.html>`_.
For convenience, that external repository duplicates the files from here in
``drivers/hid/bpf/progs`` into its own ``src/bpf/stable`` directory. This allows
distributions to not have to pull the entire kernel source tree to ship and package
those HID-BPF fixes. ``udev-hid-bpf`` also has capabilities of handling multiple
objects files depending on the kernel the user is running.
Available types of programs
===========================
HID-BPF is built "on top" of BPF, meaning that we use bpf struct_ops method to
declare our programs.
HID-BPF has the following attachment types available:
1. event processing/filtering with ``SEC("struct_ops/hid_device_event")`` in libbpf
2. actions coming from userspace with ``SEC("syscall")`` in libbpf
3. change of the report descriptor with ``SEC("struct_ops/hid_rdesc_fixup")`` or
``SEC("struct_ops.s/hid_rdesc_fixup")`` in libbpf
A ``hid_device_event`` is calling a BPF program when an event is received from
the device. Thus we are in IRQ context and can act on the data or notify userspace.
And given that we are in IRQ context, we can not talk back to the device.
A ``syscall`` means that userspace called the syscall ``BPF_PROG_RUN`` facility.
This time, we can do any operations allowed by HID-BPF, and talking to the device is
allowed.
Last, ``hid_rdesc_fixup`` is different from the others as there can be only one
BPF program of this type. This is called on ``probe`` from the driver and allows to
change the report descriptor from the BPF program. Once a ``hid_rdesc_fixup``
program has been loaded, it is not possible to overwrite it unless the program which
inserted it allows us by pinning the program and closing all of its fds pointing to it.
Note that ``hid_rdesc_fixup`` can be declared as sleepable (``SEC("struct_ops.s/hid_rdesc_fixup")``).
Developer API:
==============
Available ``struct_ops`` for HID-BPF:
-------------------------------------
.. kernel-doc:: include/linux/hid_bpf.h
:identifiers: hid_bpf_ops
User API data structures available in programs:
-----------------------------------------------
.. kernel-doc:: include/linux/hid_bpf.h
:identifiers: hid_bpf_ctx
Available API that can be used in all HID-BPF struct_ops programs:
------------------------------------------------------------------
.. kernel-doc:: drivers/hid/bpf/hid_bpf_dispatch.c
:identifiers: hid_bpf_get_data
Available API that can be used in syscall HID-BPF programs or in sleepable HID-BPF struct_ops programs:
-------------------------------------------------------------------------------------------------------
.. kernel-doc:: drivers/hid/bpf/hid_bpf_dispatch.c
:identifiers: hid_bpf_hw_request hid_bpf_hw_output_report hid_bpf_input_report hid_bpf_try_input_report hid_bpf_allocate_context hid_bpf_release_context
General overview of a HID-BPF program
=====================================
Accessing the data attached to the context
------------------------------------------
The ``struct hid_bpf_ctx`` doesn't export the ``data`` fields directly and to access
it, a bpf program needs to first call :c:func:`hid_bpf_get_data`.
``offset`` can be any integer, but ``size`` needs to be constant, known at compile
time.
This allows the following:
1. for a given device, if we know that the report length will always be of a certain value,
we can request the ``data`` pointer to point at the full report length.
The kernel will ensure we are using a correct size and offset and eBPF will ensure
the code will not attempt to read or write outside of the boundaries::
__u8 *data = hid_bpf_get_data(ctx, 0 /* offset */, 256 /* size */);
if (!data)
return 0; /* ensure data is correct, now the verifier knows we
* have 256 bytes available */
bpf_printk("hello world: %02x %02x %02x", data[0], data[128], data[255]);
2. if the report length is variable, but we know the value of ``X`` is always a 16-bit
integer, we can then have a pointer to that value only::
__u16 *x = hid_bpf_get_data(ctx, offset, sizeof(*x));
if (!x)
return 0; /* something went wrong */
*x += 1; /* increment X by one */
Effect of a HID-BPF program
---------------------------
For all HID-BPF attachment types except for :c:func:`hid_rdesc_fixup`, several eBPF
programs can be attached to the same device. If a HID-BPF struct_ops has a
:c:func:`hid_rdesc_fixup` while another is already attached to the device, the
kernel will return `-EINVAL` when attaching the struct_ops.
Unless ``BPF_F_BEFORE`` is added to the flags while attaching the program, the new
program is appended at the end of the list.
``BPF_F_BEFORE`` will insert the new program at the beginning of the list which is
useful for e.g. tracing where we need to get the unprocessed events from the device.
Note that if there are multiple programs using the ``BPF_F_BEFORE`` flag,
only the most recently loaded one is actually the first in the list.
``SEC("struct_ops/hid_device_event")``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Whenever a matching event is raised, the eBPF programs are called one after the other
and are working on the same data buffer.
If a program changes the data associated with the context, the next one will see
the modified data but it will have *no* idea of what the original data was.
Once all the programs are run and return ``0`` or a positive value, the rest of the
HID stack will work on the modified data, with the ``size`` field of the last hid_bpf_ctx
being the new size of the input stream of data.
A BPF program returning a negative error discards the event, i.e. this event will not be
processed by the HID stack. Clients (hidraw, input, LEDs) will **not** see this event.
``SEC("syscall")``
~~~~~~~~~~~~~~~~~~
``syscall`` are not attached to a given device. To tell which device we are working
with, userspace needs to refer to the device by its unique system id (the last 4 numbers
in the sysfs path: ``/sys/bus/hid/devices/xxxx:yyyy:zzzz:0000``).
To retrieve a context associated with the device, the program must call
hid_bpf_allocate_context() and must release it with hid_bpf_release_context()
before returning.
Once the context is retrieved, one can also request a pointer to kernel memory with
hid_bpf_get_data(). This memory is big enough to support all input/output/feature
reports of the given device.
``SEC("struct_ops/hid_rdesc_fixup")``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The ``hid_rdesc_fixup`` program works in a similar manner to ``.report_fixup``
of ``struct hid_driver``.
When the device is probed, the kernel sets the data buffer of the context with the
content of the report descriptor. The memory associated with that buffer is
``HID_MAX_DESCRIPTOR_SIZE`` (currently 4kB).
The eBPF program can modify the data buffer at-will and the kernel uses the
modified content and size as the report descriptor.
Whenever a struct_ops containing a ``SEC("struct_ops/hid_rdesc_fixup")`` program
is attached (if no program was attached before), the kernel immediately disconnects
the HID device and does a reprobe.
In the same way, when this struct_ops is detached, the kernel issues a disconnect
on the device.
There is no ``detach`` facility in HID-BPF. Detaching a program happens when
all the user space file descriptors pointing at a HID-BPF struct_ops link are closed.
Thus, if we need to replace a report descriptor fixup, some cooperation is
required from the owner of the original report descriptor fixup.
The previous owner will likely pin the struct_ops link in the bpffs, and we can then
replace it through normal bpf operations.
Attaching a bpf program to a device
===================================
We now use standard struct_ops attachment through ``bpf_map__attach_struct_ops()``.
But given that we need to attach a struct_ops to a dedicated HID device, the caller
must set ``hid_id`` in the struct_ops map before loading the program in the kernel.
``hid_id`` is the unique system ID of the HID device (the last 4 numbers in the
sysfs path: ``/sys/bus/hid/devices/xxxx:yyyy:zzzz:0000``)
One can also set ``flags``, which is of type ``enum hid_bpf_attach_flags``.
We can not rely on hidraw to bind a BPF program to a HID device. hidraw is an
artefact of the processing of the HID device, and is not stable. Some drivers
even disable it, so that removes the tracing capabilities on those devices
(where it is interesting to get the non-hidraw traces).
On the other hand, the ``hid_id`` is stable for the entire life of the HID device,
even if we change its report descriptor.
Given that hidraw is not stable when the device disconnects/reconnects, we recommend
accessing the current report descriptor of the device through the sysfs.
This is available at ``/sys/bus/hid/devices/BUS:VID:PID.000N/report_descriptor`` as a
binary stream.
Parsing the report descriptor is the responsibility of the BPF programmer or the userspace
component that loads the eBPF program.
An (almost) complete example of a BPF enhanced HID device
=========================================================
*Foreword: for most parts, this could be implemented as a kernel driver*
Let's imagine we have a new tablet device that has some haptic capabilities
to simulate the surface the user is scratching on. This device would also have
a specific 3 positions switch to toggle between *pencil on paper*, *cray on a wall*
and *brush on a painting canvas*. To make things even better, we can control the
physical position of the switch through a feature report.
And of course, the switch is relying on some userspace component to control the
haptic feature of the device itself.
Filtering events
----------------
The first step consists in filtering events from the device. Given that the switch
position is actually reported in the flow of the pen events, using hidraw to implement
that filtering would mean that we wake up userspace for every single event.
This is OK for libinput, but having an external library that is just interested in
one byte in the report is less than ideal.
For that, we can create a basic skeleton for our BPF program::
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
/* HID programs need to be GPL */
char _license[] SEC("license") = "GPL";
/* HID-BPF kfunc API definitions */
extern __u8 *hid_bpf_get_data(struct hid_bpf_ctx *ctx,
unsigned int offset,
const size_t __sz) __ksym;
struct {
__uint(type, BPF_MAP_TYPE_RINGBUF);
__uint(max_entries, 4096 * 64);
} ringbuf SEC(".maps");
__u8 current_value = 0;
SEC("struct_ops/hid_device_event")
int BPF_PROG(filter_switch, struct hid_bpf_ctx *hid_ctx)
{
__u8 *data = hid_bpf_get_data(hid_ctx, 0 /* offset */, 192 /* size */);
__u8 *buf;
if (!data)
return 0; /* EPERM check */
if (current_value != data[152]) {
buf = bpf_ringbuf_reserve(&ringbuf, 1, 0);
if (!buf)
return 0;
*buf = data[152];
bpf_ringbuf_commit(buf, 0);
current_value = data[152];
}
return 0;
}
SEC(".struct_ops.link")
struct hid_bpf_ops haptic_tablet = {
.hid_device_event = (void *)filter_switch,
};
To attach ``haptic_tablet``, userspace needs to set ``hid_id`` first::
static int attach_filter(struct hid *hid_skel, int hid_id)
{
int err, link_fd;
hid_skel->struct_ops.haptic_tablet->hid_id = hid_id;
err = hid__load(skel);
if (err)
return err;
link_fd = bpf_map__attach_struct_ops(hid_skel->maps.haptic_tablet);
if (!link_fd) {
fprintf(stderr, "can not attach HID-BPF program: %m\n");
return -1;
}
return link_fd; /* the fd of the created bpf_link */
}
Our userspace program can now listen to notifications on the ring buffer, and
is awaken only when the value changes.
When the userspace program doesn't need to listen to events anymore, it can just
close the returned bpf link from :c:func:`attach_filter`, which will tell the kernel to
detach the program from the HID device.
Of course, in other use cases, the userspace program can also pin the fd to the
BPF filesystem through a call to :c:func:`bpf_obj_pin`, as with any bpf_link.
Controlling the device
----------------------
To be able to change the haptic feedback from the tablet, the userspace program
needs to emit a feature report on the device itself.
Instead of using hidraw for that, we can create a ``SEC("syscall")`` program
that talks to the device::
/* some more HID-BPF kfunc API definitions */
extern struct hid_bpf_ctx *hid_bpf_allocate_context(unsigned int hid_id) __ksym;
extern void hid_bpf_release_context(struct hid_bpf_ctx *ctx) __ksym;
extern int hid_bpf_hw_request(struct hid_bpf_ctx *ctx,
__u8* data,
size_t len,
enum hid_report_type type,
enum hid_class_request reqtype) __ksym;
struct hid_send_haptics_args {
/* data needs to come at offset 0 so we can do a memcpy into it */
__u8 data[10];
unsigned int hid;
};
SEC("syscall")
int send_haptic(struct hid_send_haptics_args *args)
{
struct hid_bpf_ctx *ctx;
int ret = 0;
ctx = hid_bpf_allocate_context(args->hid);
if (!ctx)
return 0; /* EPERM check */
ret = hid_bpf_hw_request(ctx,
args->data,
10,
HID_FEATURE_REPORT,
HID_REQ_SET_REPORT);
hid_bpf_release_context(ctx);
return ret;
}
And then userspace needs to call that program directly::
static int set_haptic(struct hid *hid_skel, int hid_id, __u8 haptic_value)
{
int err, prog_fd;
int ret = -1;
struct hid_send_haptics_args args = {
.hid = hid_id,
};
DECLARE_LIBBPF_OPTS(bpf_test_run_opts, tattrs,
.ctx_in = &args,
.ctx_size_in = sizeof(args),
);
args.data[0] = 0x02; /* report ID of the feature on our device */
args.data[1] = haptic_value;
prog_fd = bpf_program__fd(hid_skel->progs.set_haptic);
err = bpf_prog_test_run_opts(prog_fd, &tattrs);
return err;
}
Now our userspace program is aware of the haptic state and can control it. The
program could make this state further available to other userspace programs
(e.g. via a DBus API).
The interesting bit here is that we did not created a new kernel API for this.
Which means that if there is a bug in our implementation, we can change the
interface with the kernel at-will, because the userspace application is
responsible for its own usage.
linux-7.2.3/Documentation/hid/hid-sensor.rst
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=====================
HID Sensors Framework
=====================
HID sensor framework provides necessary interfaces to implement sensor drivers,
which are connected to a sensor hub. The sensor hub is a HID device and it provides
a report descriptor conforming to HID 1.12 sensor usage tables.
Description from the HID 1.12 "HID Sensor Usages" specification:
"Standardization of HID usages for sensors would allow (but not require) sensor
hardware vendors to provide a consistent Plug And Play interface at the USB boundary,
thereby enabling some operating systems to incorporate common device drivers that
could be reused between vendors, alleviating any need for the vendors to provide
the drivers themselves."
This specification describes many usage IDs, which describe the type of sensor
and also the individual data fields. Each sensor can have variable number of
data fields. The length and order is specified in the report descriptor. For
example a part of report descriptor can look like::
INPUT(1)[INPUT]
..
Field(2)
Physical(0020.0073)
Usage(1)
0020.045f
Logical Minimum(-32767)
Logical Maximum(32767)
Report Size(8)
Report Count(1)
Report Offset(16)
Flags(Variable Absolute)
..
..
The report is indicating "sensor page (0x20)" contains an accelerometer-3D (0x73).
This accelerometer-3D has some fields. Here for example field 2 is motion intensity
(0x045f) with a logical minimum value of -32767 and logical maximum of 32767. The
order of fields and length of each field is important as the input event raw
data will use this format.
Implementation
==============
This specification defines many different types of sensors with different sets of
data fields. It is difficult to have a common input event to user space applications,
for different sensors. For example an accelerometer can send X,Y and Z data, whereas
an ambient light sensor can send illumination data.
So the implementation has two parts:
- Core HID driver
- Individual sensor processing part (sensor drivers)
Core driver
-----------
The core driver (hid-sensor-hub) registers as a HID driver. It parses
report descriptors and identifies all the sensors present. It adds an MFD device
with name HID-SENSOR-xxxx (where xxxx is usage id from the specification).
For example:
HID-SENSOR-200073 is registered for an Accelerometer 3D driver.
So if any driver with this name is inserted, then the probe routine for that
function will be called. So an accelerometer processing driver can register
with this name and will be probed if there is an accelerometer-3D detected.
The core driver provides a set of APIs which can be used by the processing
drivers to register and get events for that usage id. Also it provides parsing
functions, which get and set each input/feature/output report.
Individual sensor processing part (sensor drivers)
--------------------------------------------------
The processing driver will use an interface provided by the core driver to parse
the report and get the indexes of the fields and also can get events. This driver
can use IIO interface to use the standard ABI defined for a type of sensor.
Core driver Interface
=====================
Callback structure::
Each processing driver can use this structure to set some callbacks.
int (*suspend)(..): Callback when HID suspend is received
int (*resume)(..): Callback when HID resume is received
int (*capture_sample)(..): Capture a sample for one of its data fields
int (*send_event)(..): One complete event is received which can have
multiple data fields.
Registration functions::
int sensor_hub_register_callback(struct hid_sensor_hub_device *hsdev,
u32 usage_id,
struct hid_sensor_hub_callbacks *usage_callback):
Registers callbacks for a usage id. The callback functions are not allowed
to sleep::
int sensor_hub_remove_callback(struct hid_sensor_hub_device *hsdev,
u32 usage_id):
Removes callbacks for a usage id.
Parsing function::
int sensor_hub_input_get_attribute_info(struct hid_sensor_hub_device *hsdev,
u8 type,
u32 usage_id, u32 attr_usage_id,
struct hid_sensor_hub_attribute_info *info);
A processing driver can look for some field of interest and check if it exists
in a report descriptor. If it exists it will store necessary information
so that fields can be set or get individually.
These indexes avoid searching every time and getting field index to get or set.
Set Feature report::
int sensor_hub_set_feature(struct hid_sensor_hub_device *hsdev, u32 report_id,
u32 field_index, s32 value);
This interface is used to set a value for a field in feature report. For example
if there is a field report_interval, which is parsed by a call to
sensor_hub_input_get_attribute_info before, then it can directly set that
individual field::
int sensor_hub_get_feature(struct hid_sensor_hub_device *hsdev, u32 report_id,
u32 field_index, s32 *value);
This interface is used to get a value for a field in input report. For example
if there is a field report_interval, which is parsed by a call to
sensor_hub_input_get_attribute_info before, then it can directly get that
individual field value::
int sensor_hub_input_attr_get_raw_value(struct hid_sensor_hub_device *hsdev,
u32 usage_id,
u32 attr_usage_id, u32 report_id);
This is used to get a particular field value through input reports. For example
accelerometer wants to poll X axis value, then it can call this function with
the usage id of X axis. HID sensors can provide events, so this is not necessary
to poll for any field. If there is some new sample, the core driver will call
registered callback function to process the sample.
----------
HID Custom and generic Sensors
------------------------------
HID Sensor specification defines two special sensor usage types. Since they
don't represent a standard sensor, it is not possible to define using Linux IIO
type interfaces.
The purpose of these sensors is to extend the functionality or provide a
way to obfuscate the data being communicated by a sensor. Without knowing the
mapping between the data and its encapsulated form, it is difficult for
an application/driver to determine what data is being communicated by the sensor.
This allows some differentiating use cases, where vendor can provide applications.
Some common use cases are debug other sensors or to provide some events like
keyboard attached/detached or lid open/close.
To allow application to utilize these sensors, here they are exported using sysfs
attribute groups, attributes and misc device interface.
An example of this representation on sysfs::
/sys/devices/pci0000:00/INT33C2:00/i2c-0/i2c-INT33D1:00/0018:8086:09FA.0001/HID-SENSOR-2000e1.6.auto$ tree -R
.
│   ├── enable_sensor
│   │   ├── feature-0-200316
│   │   │   ├── feature-0-200316-maximum
│   │   │   ├── feature-0-200316-minimum
│   │   │   ├── feature-0-200316-name
│   │   │   ├── feature-0-200316-size
│   │   │   ├── feature-0-200316-unit-expo
│   │   │   ├── feature-0-200316-units
│   │   │   ├── feature-0-200316-value
│   │   ├── feature-1-200201
│   │   │   ├── feature-1-200201-maximum
│   │   │   ├── feature-1-200201-minimum
│   │   │   ├── feature-1-200201-name
│   │   │   ├── feature-1-200201-size
│   │   │   ├── feature-1-200201-unit-expo
│   │   │   ├── feature-1-200201-units
│   │   │   ├── feature-1-200201-value
│   │   ├── input-0-200201
│   │   │   ├── input-0-200201-maximum
│   │   │   ├── input-0-200201-minimum
│   │   │   ├── input-0-200201-name
│   │   │   ├── input-0-200201-size
│   │   │   ├── input-0-200201-unit-expo
│   │   │   ├── input-0-200201-units
│   │   │   ├── input-0-200201-value
│   │   ├── input-1-200202
│   │   │   ├── input-1-200202-maximum
│   │   │   ├── input-1-200202-minimum
│   │   │   ├── input-1-200202-name
│   │   │   ├── input-1-200202-size
│   │   │   ├── input-1-200202-unit-expo
│   │   │   ├── input-1-200202-units
│   │   │   ├── input-1-200202-value
Here there is a custom sensor with four fields: two feature and two inputs.
Each field is represented by a set of attributes. All fields except the "value"
are read only. The value field is a read-write field.
Example::
/sys/bus/platform/devices/HID-SENSOR-2000e1.6.auto/feature-0-200316$ grep -r . *
feature-0-200316-maximum:6
feature-0-200316-minimum:0
feature-0-200316-name:property-reporting-state
feature-0-200316-size:1
feature-0-200316-unit-expo:0
feature-0-200316-units:25
feature-0-200316-value:1
How to enable such sensor?
^^^^^^^^^^^^^^^^^^^^^^^^^^
By default sensor can be power gated. To enable sysfs attribute "enable" can be
used::
$ echo 1 > enable_sensor
Once enabled and powered on, sensor can report value using HID reports.
These reports are pushed using misc device interface in a FIFO order::
/dev$ tree | grep HID-SENSOR-2000e1.6.auto
│   │   │   ├── 10:53 -> ../HID-SENSOR-2000e1.6.auto
│   ├── HID-SENSOR-2000e1.6.auto
Each report can be of variable length preceded by a header. This header
consists of a 32-bit usage id, 64-bit time stamp and 32-bit length field of raw
data.
linux-7.2.3/Documentation/hid/hid-transport.rst
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=========================
HID I/O Transport Drivers
=========================
The HID subsystem is independent of the underlying transport driver. Initially,
only USB was supported, but other specifications adopted the HID design and
provided new transport drivers. The kernel includes at least support for USB,
Bluetooth, I2C and user-space I/O drivers.
1) HID Bus
==========
The HID subsystem is designed as a bus. Any I/O subsystem may provide HID
devices and register them with the HID bus. HID core then loads generic device
drivers on top of it. The transport drivers are responsible for raw data
transport and device setup/management. HID core is responsible for
report-parsing, report interpretation and the user-space API. Device specifics
and quirks are handled by all layers depending on the quirk.
::
+-----------+ +-----------+ +-----------+ +-----------+
| Device #1 | | Device #i | | Device #j | | Device #k |
+-----------+ +-----------+ +-----------+ +-----------+
\\ // \\ //
+------------+ +------------+
| I/O Driver | | I/O Driver |
+------------+ +------------+
|| ||
+------------------+ +------------------+
| Transport Driver | | Transport Driver |
+------------------+ +------------------+
\___ ___/
\ /
+----------------+
| HID Core |
+----------------+
/ | | \
/ | | \
____________/ | | \_________________
/ | | \
/ | | \
+----------------+ +-----------+ +------------------+ +------------------+
| Generic Driver | | MT Driver | | Custom Driver #1 | | Custom Driver #2 |
+----------------+ +-----------+ +------------------+ +------------------+
Example Drivers:
- I/O: USB, I2C, Bluetooth-l2cap
- Transport: USB-HID, I2C-HID, BT-HIDP
Everything below "HID Core" is simplified in this graph as it is only of
interest to HID device drivers. Transport drivers do not need to know the
specifics.
1.1) Device Setup
-----------------
I/O drivers normally provide hotplug detection or device enumeration APIs to the
transport drivers. Transport drivers use this to find any suitable HID device.
They allocate HID device objects and register them with HID core. Transport
drivers are not required to register themselves with HID core. HID core is never
aware of which transport drivers are available and is not interested in it. It
is only interested in devices.
Transport drivers attach a constant "struct hid_ll_driver" object with each
device. Once a device is registered with HID core, the callbacks provided via
this struct are used by HID core to communicate with the device.
Transport drivers are responsible for detecting device failures and unplugging.
HID core will operate a device as long as it is registered regardless of any
device failures. Once transport drivers detect unplug or failure events, they
must unregister the device from HID core and HID core will stop using the
provided callbacks.
1.2) Transport Driver Requirements
----------------------------------
The terms "asynchronous" and "synchronous" in this document describe the
transmission behavior regarding acknowledgements. An asynchronous channel must
not perform any synchronous operations like waiting for acknowledgements or
verifications. Generally, HID calls operating on asynchronous channels must be
running in atomic-context just fine.
On the other hand, synchronous channels can be implemented by the transport
driver in whatever way they like. They might just be the same as asynchronous
channels, but they can also provide acknowledgement reports, automatic
retransmission on failure, etc. in a blocking manner. If such functionality is
required on asynchronous channels, a transport-driver must implement that via
its own worker threads.
HID core requires transport drivers to follow a given design. A Transport
driver must provide two bi-directional I/O channels to each HID device. These
channels must not necessarily be bi-directional in the hardware itself. A
transport driver might just provide 4 uni-directional channels. Or it might
multiplex all four on a single physical channel. However, in this document we
will describe them as two bi-directional channels as they have several
properties in common.
- Interrupt Channel (intr): The intr channel is used for asynchronous data
reports. No management commands or data acknowledgements are sent on this
channel. Any unrequested incoming or outgoing data report must be sent on
this channel and is never acknowledged by the remote side. Devices usually
send their input events on this channel. Outgoing events are normally
not sent via intr, except if high throughput is required.
- Control Channel (ctrl): The ctrl channel is used for synchronous requests and
device management. Unrequested data input events must not be sent on this
channel and are normally ignored. Instead, devices only send management
events or answers to host requests on this channel.
The control-channel is used for direct blocking queries to the device
independent of any events on the intr-channel.
Outgoing reports are usually sent on the ctrl channel via synchronous
SET_REPORT requests.
Communication between devices and HID core is mostly done via HID reports. A
report can be of one of three types:
- INPUT Report: Input reports provide data from device to host. This
data may include button events, axis events, battery status or more. This
data is generated by the device and sent to the host with or without
requiring explicit requests. Devices can choose to send data continuously or
only on change.
- OUTPUT Report: Output reports change device states. They are sent from host
to device and may include LED requests, rumble requests or more. Output
reports are never sent from device to host, but a host can retrieve their
current state.
Hosts may choose to send output reports either continuously or only on
change.
- FEATURE Report: Feature reports are used for specific static device features
and never reported spontaneously. A host can read and/or write them to access
data like battery-state or device-settings.
Feature reports are never sent without requests. A host must explicitly set
or retrieve a feature report. This also means, feature reports are never sent
on the intr channel as this channel is asynchronous.
INPUT and OUTPUT reports can be sent as pure data reports on the intr channel.
For INPUT reports this is the usual operational mode. But for OUTPUT reports,
this is rarely done as OUTPUT reports are normally quite scarce. But devices are
free to make excessive use of asynchronous OUTPUT reports (for instance, custom
HID audio speakers make great use of it).
Plain reports must not be sent on the ctrl channel, though. Instead, the ctrl
channel provides synchronous GET/SET_REPORT requests. Plain reports are only
allowed on the intr channel and are the only means of data there.
- GET_REPORT: A GET_REPORT request has a report ID as payload and is sent
from host to device. The device must answer with a data report for the
requested report ID on the ctrl channel as a synchronous acknowledgement.
Only one GET_REPORT request can be pending for each device. This restriction
is enforced by HID core as several transport drivers don't allow multiple
simultaneous GET_REPORT requests.
Note that data reports which are sent as answer to a GET_REPORT request are
not handled as generic device events. That is, if a device does not operate
in continuous data reporting mode, an answer to GET_REPORT does not replace
the raw data report on the intr channel on state change.
GET_REPORT is only used by custom HID device drivers to query device state.
Normally, HID core caches any device state so this request is not necessary
on devices that follow the HID specs except during device initialization to
retrieve the current state.
GET_REPORT requests can be sent for any of the 3 report types and shall
return the current report state of the device. However, OUTPUT reports as
payload may be blocked by the underlying transport driver if the
specification does not allow them.
- SET_REPORT: A SET_REPORT request has a report ID plus data as payload. It is
sent from host to device and a device must update its current report state
according to the given data. Any of the 3 report types can be used. However,
INPUT reports as payload might be blocked by the underlying transport driver
if the specification does not allow them.
A device must answer with a synchronous acknowledgement. However, HID core
does not require transport drivers to forward this acknowledgement to HID
core.
Same as for GET_REPORT, only one SET_REPORT can be pending at a time. This
restriction is enforced by HID core as some transport drivers do not support
multiple synchronous SET_REPORT requests.
Other ctrl-channel requests are supported by USB-HID but are not available
(or deprecated) in most other transport level specifications:
- GET/SET_IDLE: Only used by USB-HID and I2C-HID.
- GET/SET_PROTOCOL: Not used by HID core.
- RESET: Used by I2C-HID, not hooked up in HID core.
- SET_POWER: Used by I2C-HID, not hooked up in HID core.
2) HID API
==========
2.1) Initialization
-------------------
Transport drivers normally use the following procedure to register a new device
with HID core::
struct hid_device *hid;
int ret;
hid = hid_allocate_device();
if (IS_ERR(hid)) {
ret = PTR_ERR(hid);
goto err_<...>;
}
strscpy(hid->name, <device-name-src>, sizeof(hid->name));
strscpy(hid->phys, <device-phys-src>, sizeof(hid->phys));
strscpy(hid->uniq, <device-uniq-src>, sizeof(hid->uniq));
hid->ll_driver = &custom_ll_driver;
hid->bus = <device-bus>;
hid->vendor = <device-vendor>;
hid->product = <device-product>;
hid->version = <device-version>;
hid->country = <device-country>;
hid->dev.parent = <pointer-to-parent-device>;
hid->driver_data = <transport-driver-data-field>;
ret = hid_add_device(hid);
if (ret)
goto err_<...>;
Once hid_add_device() is entered, HID core might use the callbacks provided in
"custom_ll_driver". Note that fields like "country" can be ignored by underlying
transport-drivers if not supported.
To unregister a device, use::
hid_destroy_device(hid);
Once hid_destroy_device() returns, HID core will no longer make use of any
driver callbacks.
2.2) hid_ll_driver operations
-----------------------------
The available HID callbacks are:
::
int (*start) (struct hid_device *hdev)
Called from HID device drivers once they want to use the device. Transport
drivers can choose to setup their device in this callback. However, normally
devices are already set up before transport drivers register them to HID core
so this is mostly only used by USB-HID.
::
void (*stop) (struct hid_device *hdev)
Called from HID device drivers once they are done with a device. Transport
drivers can free any buffers and deinitialize the device. But note that
->start() might be called again if another HID device driver is loaded on the
device.
Transport drivers are free to ignore it and deinitialize devices after they
destroyed them via hid_destroy_device().
::
int (*open) (struct hid_device *hdev)
Called from HID device drivers once they are interested in data reports.
Usually, while user-space didn't open any input API/etc., device drivers are
not interested in device data and transport drivers can put devices asleep.
However, once ->open() is called, transport drivers must be ready for I/O.
->open() calls are nested for each client that opens the HID device.
::
void (*close) (struct hid_device *hdev)
Called from HID device drivers after ->open() was called but they are no
longer interested in device reports. (Usually if user-space closed any input
devices of the driver).
Transport drivers can put devices asleep and terminate any I/O of all
->open() calls have been followed by a ->close() call. However, ->start() may
be called again if the device driver is interested in input reports again.
::
int (*parse) (struct hid_device *hdev)
Called once during device setup after ->start() has been called. Transport
drivers must read the HID report-descriptor from the device and tell HID core
about it via hid_parse_report().
::
int (*power) (struct hid_device *hdev, int level)
Called by HID core to give PM hints to transport drivers. Usually this is
analogical to the ->open() and ->close() hints and redundant.
::
void (*request) (struct hid_device *hdev, struct hid_report *report,
int reqtype)
Send a HID request on the ctrl channel. "report" contains the report that
should be sent and "reqtype" the request type. Request-type can be
HID_REQ_SET_REPORT or HID_REQ_GET_REPORT.
This callback is optional. If not provided, HID core will assemble a raw
report following the HID specs and send it via the ->raw_request() callback.
The transport driver is free to implement this asynchronously.
::
int (*wait) (struct hid_device *hdev)
Used by HID core before calling ->request() again. A transport driver can use
it to wait for any pending requests to complete if only one request is
allowed at a time.
::
int (*raw_request) (struct hid_device *hdev, unsigned char reportnum,
__u8 *buf, size_t count, unsigned char rtype,
int reqtype)
Same as ->request() but provides the report as raw buffer. This request shall
be synchronous. A transport driver must not use ->wait() to complete such
requests. This request is mandatory and hid core will reject the device if
it is missing.
::
int (*output_report) (struct hid_device *hdev, __u8 *buf, size_t len)
Send raw output report via intr channel. Used by some HID device drivers
which require high throughput for outgoing requests on the intr channel. This
must not cause SET_REPORT calls! This must be implemented as asynchronous
output report on the intr channel!
::
int (*idle) (struct hid_device *hdev, int report, int idle, int reqtype)
Perform SET/GET_IDLE request. Only used by USB-HID, do not implement!
2.3) Data Path
--------------
Transport drivers are responsible of reading data from I/O devices. They must
handle any I/O-related state-tracking themselves. HID core does not implement
protocol handshakes or other management commands which can be required by the
given HID transport specification.
Every raw data packet read from a device must be fed into HID core via
hid_input_report(). You must specify the channel-type (intr or ctrl) and report
type (input/output/feature). Under normal conditions, only input reports are
provided via this API.
Responses to GET_REPORT requests via ->request() must also be provided via this
API. Responses to ->raw_request() are synchronous and must be intercepted by the
transport driver and not passed to hid_input_report().
Acknowledgements to SET_REPORT requests are not of interest to HID core.
----------------------------------------------------
Written 2013, David Herrmann <dh.herrmann@gmail.com>
linux-7.2.3/Documentation/hid/hiddev.rst
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================================================
Care and feeding of your Human Interface Devices
================================================
Introduction
============
In addition to the normal input type HID devices, USB also uses the
human interface device protocols for things that are not really human
interfaces, but have similar sorts of communication needs. The two big
examples for this are power devices (especially uninterruptible power
supplies) and monitor control on higher end monitors.
To support these disparate requirements, the Linux USB system provides
HID events to two separate interfaces:
* the input subsystem, which converts HID events into normal input
device interfaces (such as keyboard, mouse and joystick) and a
normalised event interface - see Documentation/input/input.rst
* the hiddev interface, which provides fairly raw HID events
The data flow for a HID event produced by a device is something like
the following::
usb.c ---> hid-core.c ----> hid-input.c ----> [keyboard/mouse/joystick/event]
|
|
--> hiddev.c ----> POWER / MONITOR CONTROL
In addition, other subsystems (apart from USB) can potentially feed
events into the input subsystem, but these have no effect on the HID
device interface.
Using the HID Device Interface
==============================
The hiddev interface is a char interface using the normal USB major,
with the minor numbers starting at 96 and finishing at 111. Therefore,
you need the following commands::
mknod /dev/usb/hiddev0 c 180 96
mknod /dev/usb/hiddev1 c 180 97
mknod /dev/usb/hiddev2 c 180 98
mknod /dev/usb/hiddev3 c 180 99
mknod /dev/usb/hiddev4 c 180 100
mknod /dev/usb/hiddev5 c 180 101
mknod /dev/usb/hiddev6 c 180 102
mknod /dev/usb/hiddev7 c 180 103
mknod /dev/usb/hiddev8 c 180 104
mknod /dev/usb/hiddev9 c 180 105
mknod /dev/usb/hiddev10 c 180 106
mknod /dev/usb/hiddev11 c 180 107
mknod /dev/usb/hiddev12 c 180 108
mknod /dev/usb/hiddev13 c 180 109
mknod /dev/usb/hiddev14 c 180 110
mknod /dev/usb/hiddev15 c 180 111
So you point your hiddev compliant user-space program at the correct
interface for your device, and it all just works.
Assuming that you have a hiddev compliant user-space program, of
course. If you need to write one, read on.
The HIDDEV API
==============
This description should be read in conjunction with the HID
specification, freely available from https://www.usb.org, and
conveniently linked of http://www.linux-usb.org.
The hiddev API uses a read() interface, and a set of ioctl() calls.
HID devices exchange data with the host computer using data
bundles called "reports". Each report is divided into "fields",
each of which can have one or more "usages". In the hid-core,
each one of these usages has a single signed 32-bit value.
read():
-------
This is the event interface. When the HID device's state changes,
it performs an interrupt transfer containing a report which contains
the changed value. The hid-core.c module parses the report, and
returns to hiddev.c the individual usages that have changed within
the report. In its basic mode, the hiddev will make these individual
usage changes available to the reader using a struct hiddev_event::
struct hiddev_event {
unsigned hid;
signed int value;
};
containing the HID usage identifier for the status that changed, and
the value that it was changed to. Note that the structure is defined
within <linux/hiddev.h>, along with some other useful #defines and
structures. The HID usage identifier is a composite of the HID usage
page shifted to the 16 high order bits ORed with the usage code. The
behavior of the read() function can be modified using the HIDIOCSFLAG
ioctl() described below.
ioctl():
--------
This is the control interface. There are a number of controls:
HIDIOCGVERSION
- int (read)
Gets the version code out of the hiddev driver.
HIDIOCAPPLICATION
- (none)
This ioctl call returns the HID application usage associated with the
HID device. The third argument to ioctl() specifies which application
index to get. This is useful when the device has more than one
application collection. If the index is invalid (greater or equal to
the number of application collections this device has) the ioctl
returns -1. You can find out beforehand how many application
collections the device has from the num_applications field from the
hiddev_devinfo structure.
HIDIOCGCOLLECTIONINFO
- struct hiddev_collection_info (read/write)
This returns a superset of the information above, providing not only
application collections, but all the collections the device has. It
also returns the level the collection lives in the hierarchy.
The user passes in a hiddev_collection_info struct with the index
field set to the index that should be returned. The ioctl fills in
the other fields. If the index is larger than the last collection
index, the ioctl returns -1 and sets errno to -EINVAL.
HIDIOCGDEVINFO
- struct hiddev_devinfo (read)
Gets a hiddev_devinfo structure which describes the device.
HIDIOCGSTRING
- struct hiddev_string_descriptor (read/write)
Gets a string descriptor from the device. The caller must fill in the
"index" field to indicate which descriptor should be returned.
HIDIOCINITREPORT
- (none)
Instructs the kernel to retrieve all input and feature report values
from the device. At this point, all the usage structures will contain
current values for the device, and will maintain it as the device
changes. Note that the use of this ioctl is unnecessary in general,
since later kernels automatically initialize the reports from the
device at attach time.
HIDIOCGNAME
- string (variable length)
Gets the device name
HIDIOCGREPORT
- struct hiddev_report_info (write)
Instructs the kernel to get a feature or input report from the device,
in order to selectively update the usage structures (in contrast to
INITREPORT).
HIDIOCSREPORT
- struct hiddev_report_info (write)
Instructs the kernel to send a report to the device. This report can
be filled in by the user through HIDIOCSUSAGE calls (below) to fill in
individual usage values in the report before sending the report in full
to the device.
HIDIOCGREPORTINFO
- struct hiddev_report_info (read/write)
Fills in a hiddev_report_info structure for the user. The report is
looked up by type (input, output or feature) and id, so these fields
must be filled in by the user. The ID can be absolute -- the actual
report id as reported by the device -- or relative --
HID_REPORT_ID_FIRST for the first report, and (HID_REPORT_ID_NEXT |
report_id) for the next report after report_id. Without a priori
information about report ids, the right way to use this ioctl is to
use the relative IDs above to enumerate the valid IDs. The ioctl
returns non-zero when there is no more next ID. The real report ID is
filled into the returned hiddev_report_info structure.
HIDIOCGFIELDINFO
- struct hiddev_field_info (read/write)
Returns the field information associated with a report in a
hiddev_field_info structure. The user must fill in report_id and
report_type in this structure, as above. The field_index should also
be filled in, which should be a number from 0 and maxfield-1, as
returned from a previous HIDIOCGREPORTINFO call.
HIDIOCGUCODE
- struct hiddev_usage_ref (read/write)
Returns the usage_code in a hiddev_usage_ref structure, given that
its report type, report id, field index, and index within the
field have already been filled into the structure.
HIDIOCGUSAGE
- struct hiddev_usage_ref (read/write)
Returns the value of a usage in a hiddev_usage_ref structure. The
usage to be retrieved can be specified as above, or the user can
choose to fill in the report_type field and specify the report_id as
HID_REPORT_ID_UNKNOWN. In this case, the hiddev_usage_ref will be
filled in with the report and field information associated with this
usage if it is found.
HIDIOCSUSAGE
- struct hiddev_usage_ref (write)
Sets the value of a usage in an output report. The user fills in
the hiddev_usage_ref structure as above, but additionally fills in
the value field.
HIDIOGCOLLECTIONINDEX
- struct hiddev_usage_ref (write)
Returns the collection index associated with this usage. This
indicates where in the collection hierarchy this usage sits.
HIDIOCGFLAG
- int (read)
HIDIOCSFLAG
- int (write)
These operations respectively inspect and replace the mode flags
that influence the read() call above. The flags are as follows:
HIDDEV_FLAG_UREF
- read() calls will now return
struct hiddev_usage_ref instead of struct hiddev_event.
This is a larger structure, but in situations where the
device has more than one usage in its reports with the
same usage code, this mode serves to resolve such
ambiguity.
HIDDEV_FLAG_REPORT
- This flag can only be used in conjunction
with HIDDEV_FLAG_UREF. With this flag set, when the device
sends a report, a struct hiddev_usage_ref will be returned
to read() filled in with the report_type and report_id, but
with field_index set to FIELD_INDEX_NONE. This serves as
additional notification when the device has sent a report.
linux-7.2.3/Documentation/hid/hidintro.rst
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.. SPDX-License-Identifier: GPL-2.0
======================================
Introduction to HID report descriptors
======================================
This chapter is meant to give a broad overview of what HID report
descriptors are, and of how a casual (non-kernel) programmer can deal
with HID devices that are not working well with Linux.
.. contents::
:local:
:depth: 2
.. toctree::
:maxdepth: 2
hidreport-parsing
Introduction
============
HID stands for Human Interface Device, and can be whatever device you
are using to interact with a computer, be it a mouse, a touchpad, a
tablet, a microphone.
Many HID devices work out the box, even if their hardware is different.
For example, mice can have any number of buttons; they may have a
wheel; movement sensitivity differs between different models, and so
on. Nonetheless, most of the time everything just works, without the
need to have specialized code in the kernel for every mouse model
developed since 1970.
This is because modern HID devices do advertise their capabilities
through the *HID report descriptor*, a fixed set of bytes describing
exactly what *HID reports* may be sent between the device and the host
and the meaning of each individual bit in those reports. For example,
a HID Report Descriptor may specify that "in a report with ID 3 the
bits from 8 to 15 is the delta x coordinate of a mouse".
The HID report itself then merely carries the actual data values
without any extra meta information. Note that HID reports may be sent
from the device ("Input Reports", i.e. input events), to the device
("Output Reports" to e.g. change LEDs) or used for device configuration
("Feature reports"). A device may support one or more HID reports.
The HID subsystem is in charge of parsing the HID report descriptors,
and converts HID events into normal input device interfaces (see
Documentation/hid/hid-transport.rst). Devices may misbehave because the
HID report descriptor provided by the device is wrong, or because it
needs to be dealt with in a special way, or because some special
device or interaction mode is not handled by the default code.
The format of HID report descriptors is described by two documents,
available from the `USB Implementers Forum <https://www.usb.org/>`_
`HID web page <https://www.usb.org/hid>`_ address:
* the `HID USB Device Class Definition
<https://www.usb.org/document-library/device-class-definition-hid-111>`_ (HID Spec from now on)
* the `HID Usage Tables <https://usb.org/document-library/hid-usage-tables-14>`_ (HUT from now on)
The HID subsystem can deal with different transport drivers
(USB, I2C, Bluetooth, etc.). See Documentation/hid/hid-transport.rst.
Parsing HID report descriptors
==============================
The current list of HID devices can be found at ``/sys/bus/hid/devices/``.
For each device, say ``/sys/bus/hid/devices/0003\:093A\:2510.0002/``,
one can read the corresponding report descriptor::
$ hexdump -C /sys/bus/hid/devices/0003\:093A\:2510.0002/report_descriptor
00000000 05 01 09 02 a1 01 09 01 a1 00 05 09 19 01 29 03 |..............).|
00000010 15 00 25 01 75 01 95 03 81 02 75 05 95 01 81 01 |..%.u.....u.....|
00000020 05 01 09 30 09 31 09 38 15 81 25 7f 75 08 95 03 |...0.1.8..%.u...|
00000030 81 06 c0 c0 |....|
00000034
Optional: the HID report descriptor can be read also by
directly accessing the hidraw driver [#hidraw]_.
The basic structure of HID report descriptors is defined in the HID
spec, while HUT "defines constants that can be interpreted by an
application to identify the purpose and meaning of a data field in a
HID report". Each entry is defined by at least two bytes, where the
first one defines what type of value is following and is described in
the HID spec, while the second one carries the actual value and is
described in the HUT.
HID report descriptors can, in principle, be painstakingly parsed by
hand, byte by byte.
A short introduction on how to do this is sketched in
Documentation/hid/hidreport-parsing.rst; you only need to understand it
if you need to patch HID report descriptors.
In practice you should not parse HID report descriptors by hand; rather,
you should use an existing parser. Among all the available ones
* the online `USB Descriptor and Request Parser
<http://eleccelerator.com/usbdescreqparser/>`_;
* `hidrdd <https://github.com/abend0c1/hidrdd>`_,
that provides very detailed and somewhat verbose descriptions
(verbosity can be useful if you are not familiar with HID report
descriptors);
* `hid-tools <https://gitlab.freedesktop.org/libevdev/hid-tools>`_,
a complete utility set that allows, among other things,
to record and replay the raw HID reports and to debug
and replay HID devices.
It is being actively developed by the Linux HID subsystem maintainers.
Parsing the mouse HID report descriptor with `hid-tools
<https://gitlab.freedesktop.org/libevdev/hid-tools>`_ leads to
(explanations interposed)::
$ ./hid-decode /sys/bus/hid/devices/0003\:093A\:2510.0002/report_descriptor
# device 0:0
# 0x05, 0x01, // Usage Page (Generic Desktop) 0
# 0x09, 0x02, // Usage (Mouse) 2
# 0xa1, 0x01, // Collection (Application) 4
# 0x09, 0x01, // Usage (Pointer) 6
# 0xa1, 0x00, // Collection (Physical) 8
# 0x05, 0x09, // Usage Page (Button) 10
what follows is a button ::
# 0x19, 0x01, // Usage Minimum (1) 12
# 0x29, 0x03, // Usage Maximum (3) 14
first button is button number 1, last button is button number 3 ::
# 0x15, 0x00, // Logical Minimum (0) 16
# 0x25, 0x01, // Logical Maximum (1) 18
each button can send values from 0 up to including 1
(i.e. they are binary buttons) ::
# 0x75, 0x01, // Report Size (1) 20
each button is sent as exactly one bit ::
# 0x95, 0x03, // Report Count (3) 22
and there are three of those bits (matching the three buttons) ::
# 0x81, 0x02, // Input (Data,Var,Abs) 24
it's actual Data (not constant padding), they represent
a single variable (Var) and their values are Absolute (not relative);
See HID spec Sec. 6.2.2.5 "Input, Output, and Feature Items" ::
# 0x75, 0x05, // Report Size (5) 26
five additional padding bits, needed to reach a byte ::
# 0x95, 0x01, // Report Count (1) 28
those five bits are repeated only once ::
# 0x81, 0x01, // Input (Cnst,Arr,Abs) 30
and take Constant (Cnst) values i.e. they can be ignored. ::
# 0x05, 0x01, // Usage Page (Generic Desktop) 32
# 0x09, 0x30, // Usage (X) 34
# 0x09, 0x31, // Usage (Y) 36
# 0x09, 0x38, // Usage (Wheel) 38
The mouse has also two physical positions (Usage (X), Usage (Y))
and a wheel (Usage (Wheel)) ::
# 0x15, 0x81, // Logical Minimum (-127) 40
# 0x25, 0x7f, // Logical Maximum (127) 42
each of them can send values ranging from -127 up to including 127 ::
# 0x75, 0x08, // Report Size (8) 44
which is represented by eight bits ::
# 0x95, 0x03, // Report Count (3) 46
and there are three of those eight bits, matching X, Y and Wheel. ::
# 0x81, 0x06, // Input (Data,Var,Rel) 48
This time the data values are Relative (Rel), i.e. they represent
the change from the previously sent report (event) ::
# 0xc0, // End Collection 50
# 0xc0, // End Collection 51
#
R: 52 05 01 09 02 a1 01 09 01 a1 00 05 09 19 01 29 03 15 00 25 01 75 01 95 03 81 02 75 05 95 01 81 01 05 01 09 30 09 31 09 38 15 81 25 7f 75 08 95 03 81 06 c0 c0
N: device 0:0
I: 3 0001 0001
This Report Descriptor tells us that the mouse input will be
transmitted using four bytes: the first one for the buttons (three
bits used, five for padding), the last three for the mouse X, Y and
wheel changes, respectively.
Indeed, for any event, the mouse will send a *report* of four bytes.
We can check the values sent by resorting e.g. to the `hid-recorder`
tool, from `hid-tools <https://gitlab.freedesktop.org/libevdev/hid-tools>`_:
The sequence of bytes sent by clicking and releasing button 1, then button 2, then button 3 is::
$ sudo ./hid-recorder /dev/hidraw1
....
output of hid-decode
....
# Button: 1 0 0 | # | X: 0 | Y: 0 | Wheel: 0
E: 000000.000000 4 01 00 00 00
# Button: 0 0 0 | # | X: 0 | Y: 0 | Wheel: 0
E: 000000.183949 4 00 00 00 00
# Button: 0 1 0 | # | X: 0 | Y: 0 | Wheel: 0
E: 000001.959698 4 02 00 00 00
# Button: 0 0 0 | # | X: 0 | Y: 0 | Wheel: 0
E: 000002.103899 4 00 00 00 00
# Button: 0 0 1 | # | X: 0 | Y: 0 | Wheel: 0
E: 000004.855799 4 04 00 00 00
# Button: 0 0 0 | # | X: 0 | Y: 0 | Wheel: 0
E: 000005.103864 4 00 00 00 00
This example shows that when button 2 is clicked,
the bytes ``02 00 00 00`` are sent, and the immediately subsequent
event (``00 00 00 00``) is the release of button 2 (no buttons are
pressed, remember that the data values are *absolute*).
If instead one clicks and holds button 1, then clicks and holds button
2, releases button 1, and finally releases button 2, the reports are::
# Button: 1 0 0 | # | X: 0 | Y: 0 | Wheel: 0
E: 000044.175830 4 01 00 00 00
# Button: 1 1 0 | # | X: 0 | Y: 0 | Wheel: 0
E: 000045.975997 4 03 00 00 00
# Button: 0 1 0 | # | X: 0 | Y: 0 | Wheel: 0
E: 000047.407930 4 02 00 00 00
# Button: 0 0 0 | # | X: 0 | Y: 0 | Wheel: 0
E: 000049.199919 4 00 00 00 00
where with ``03 00 00 00`` both buttons are pressed, and with the
subsequent ``02 00 00 00`` button 1 is released while button 2 is still
active.
Output, Input and Feature Reports
---------------------------------
HID devices can have Input Reports, like in the mouse example, Output
Reports, and Feature Reports. "Output" means that the information is
sent to the device. For example, a joystick with force feedback will
have some output; the led of a keyboard would need an output as well.
"Input" means that data come from the device.
"Feature"s are not meant to be consumed by the end user and define
configuration options for the device. They can be queried from the host;
when declared as *Volatile* they should be changed by the host.
Collections, Report IDs and Evdev events
========================================
A single device can logically group data into different independent
sets, called a *Collection*. Collections can be nested and there are
different types of collections (see the HID spec 6.2.2.6
"Collection, End Collection Items" for details).
Different reports are identified by means of different *Report ID*
fields, i.e. a number identifying the structure of the immediately
following report.
Whenever a Report ID is needed it is transmitted as the first byte of
any report. A device with only one supported HID report (like the mouse
example above) may omit the report ID.
Consider the following HID report descriptor::
05 01 09 02 A1 01 85 01 05 09 19 01 29 05 15 00
25 01 95 05 75 01 81 02 95 01 75 03 81 01 05 01
09 30 09 31 16 00 F8 26 FF 07 75 0C 95 02 81 06
09 38 15 80 25 7F 75 08 95 01 81 06 05 0C 0A 38
02 15 80 25 7F 75 08 95 01 81 06 C0 05 01 09 02
A1 01 85 02 05 09 19 01 29 05 15 00 25 01 95 05
75 01 81 02 95 01 75 03 81 01 05 01 09 30 09 31
16 00 F8 26 FF 07 75 0C 95 02 81 06 09 38 15 80
25 7F 75 08 95 01 81 06 05 0C 0A 38 02 15 80 25
7F 75 08 95 01 81 06 C0 05 01 09 07 A1 01 85 05
05 07 15 00 25 01 09 29 09 3E 09 4B 09 4E 09 E3
09 E8 09 E8 09 E8 75 01 95 08 81 02 95 00 81 01
C0 05 0C 09 01 A1 01 85 06 15 00 25 01 75 01 95
01 09 3F 81 06 09 3F 81 06 09 3F 81 06 09 3F 81
06 09 3F 81 06 09 3F 81 06 09 3F 81 06 09 3F 81
06 C0 05 0C 09 01 A1 01 85 03 09 05 15 00 26 FF
00 75 08 95 02 B1 02 C0
After parsing it (try to parse it on your own using the suggested
tools!) one can see that the device presents two ``Mouse`` Application
Collections (with reports identified by Reports IDs 1 and 2,
respectively), a ``Keypad`` Application Collection (whose report is
identified by the Report ID 5) and two ``Consumer Controls`` Application
Collections, (with Report IDs 6 and 3, respectively). Note, however,
that a device can have different Report IDs for the same Application
Collection.
The data sent will begin with the Report ID byte, and will be followed
by the corresponding information. For example, the data transmitted for
the last consumer control::
0x05, 0x0C, // Usage Page (Consumer)
0x09, 0x01, // Usage (Consumer Control)
0xA1, 0x01, // Collection (Application)
0x85, 0x03, // Report ID (3)
0x09, 0x05, // Usage (Headphone)
0x15, 0x00, // Logical Minimum (0)
0x26, 0xFF, 0x00, // Logical Maximum (255)
0x75, 0x08, // Report Size (8)
0x95, 0x02, // Report Count (2)
0xB1, 0x02, // Feature (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position,Non-volatile)
0xC0, // End Collection
will be of three bytes: the first for the Report ID (3), the next two
for the headphone, with two (``Report Count (2)``) bytes
(``Report Size (8)``), each ranging from 0 (``Logical Minimum (0)``)
to 255 (``Logical Maximum (255)``).
All the Input data sent by the device should be translated into
corresponding Evdev events, so that the remaining part of the stack can
know what is going on, e.g. the bit for the first button translates into
the ``EV_KEY/BTN_LEFT`` evdev event and relative X movement translates
into the ``EV_REL/REL_X`` evdev event".
Events
======
In Linux, one ``/dev/input/event*`` is created for each ``Application
Collection``. Going back to the mouse example, and repeating the
sequence where one clicks and holds button 1, then clicks and holds
button 2, releases button 1, and finally releases button 2, one gets::
$ sudo libinput record /dev/input/event1
# libinput record
version: 1
ndevices: 1
libinput:
version: "1.23.0"
git: "unknown"
system:
os: "opensuse-tumbleweed:20230619"
kernel: "6.3.7-1-default"
dmi: "dmi:bvnHP:bvrU77Ver.01.05.00:bd03/24/2022:br5.0:efr20.29:svnHP:pnHPEliteBook64514inchG9NotebookPC:pvr:rvnHP:rn89D2:rvrKBCVersion14.1D.00:cvnHP:ct10:cvr:sku5Y3J1EA#ABZ:"
devices:
- node: /dev/input/event1
evdev:
# Name: PixArt HP USB Optical Mouse
# ID: bus 0x3 vendor 0x3f0 product 0x94a version 0x111
# Supported Events:
# Event type 0 (EV_SYN)
# Event type 1 (EV_KEY)
# Event code 272 (BTN_LEFT)
# Event code 273 (BTN_RIGHT)
# Event code 274 (BTN_MIDDLE)
# Event type 2 (EV_REL)
# Event code 0 (REL_X)
# Event code 1 (REL_Y)
# Event code 8 (REL_WHEEL)
# Event code 11 (REL_WHEEL_HI_RES)
# Event type 4 (EV_MSC)
# Event code 4 (MSC_SCAN)
# Properties:
name: "PixArt HP USB Optical Mouse"
id: [3, 1008, 2378, 273]
codes:
0: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15] # EV_SYN
1: [272, 273, 274] # EV_KEY
2: [0, 1, 8, 11] # EV_REL
4: [4] # EV_MSC
properties: []
hid: [
0x05, 0x01, 0x09, 0x02, 0xa1, 0x01, 0x09, 0x01, 0xa1, 0x00, 0x05, 0x09, 0x19, 0x01, 0x29, 0x03,
0x15, 0x00, 0x25, 0x01, 0x95, 0x08, 0x75, 0x01, 0x81, 0x02, 0x05, 0x01, 0x09, 0x30, 0x09, 0x31,
0x09, 0x38, 0x15, 0x81, 0x25, 0x7f, 0x75, 0x08, 0x95, 0x03, 0x81, 0x06, 0xc0, 0xc0
]
udev:
properties:
- ID_INPUT=1
- ID_INPUT_MOUSE=1
- LIBINPUT_DEVICE_GROUP=3/3f0/94a:usb-0000:05:00.3-2
quirks:
events:
# Current time is 12:31:56
- evdev:
- [ 0, 0, 4, 4, 30] # EV_MSC / MSC_SCAN 30 (obfuscated)
- [ 0, 0, 1, 272, 1] # EV_KEY / BTN_LEFT 1
- [ 0, 0, 0, 0, 0] # ------------ SYN_REPORT (0) ---------- +0ms
- evdev:
- [ 1, 207892, 4, 4, 30] # EV_MSC / MSC_SCAN 30 (obfuscated)
- [ 1, 207892, 1, 273, 1] # EV_KEY / BTN_RIGHT 1
- [ 1, 207892, 0, 0, 0] # ------------ SYN_REPORT (0) ---------- +1207ms
- evdev:
- [ 2, 367823, 4, 4, 30] # EV_MSC / MSC_SCAN 30 (obfuscated)
- [ 2, 367823, 1, 272, 0] # EV_KEY / BTN_LEFT 0
- [ 2, 367823, 0, 0, 0] # ------------ SYN_REPORT (0) ---------- +1160ms
# Current time is 12:32:00
- evdev:
- [ 3, 247617, 4, 4, 30] # EV_MSC / MSC_SCAN 30 (obfuscated)
- [ 3, 247617, 1, 273, 0] # EV_KEY / BTN_RIGHT 0
- [ 3, 247617, 0, 0, 0] # ------------ SYN_REPORT (0) ---------- +880ms
Note: if ``libinput record`` is not available on your system try using
``evemu-record``.
When something does not work
============================
There can be a number of reasons why a device does not behave
correctly. For example
* The HID report descriptor provided by the HID device may be wrong
because e.g.
* it does not follow the standard, so that the kernel
will not able to make sense of the HID report descriptor;
* the HID report descriptor *does not match* what is actually
sent by the device (this can be verified by reading the raw HID
data);
* the HID report descriptor may need some "quirks" (see later on).
As a consequence, a ``/dev/input/event*`` may not be created
for each Application Collection, and/or the events
there may not match what you would expect.
Quirks
------
There are some known peculiarities of HID devices that the kernel
knows how to fix - these are called the HID quirks and a list of those
is available in `include/linux/hid.h`.
Should this be the case, it should be enough to add the required quirk
in the kernel, for the HID device at hand. This can be done in the file
`drivers/hid/hid-quirks.c`. How to do it should be relatively
straightforward after looking into the file.
The list of currently defined quirks, from `include/linux/hid.h`, is
.. kernel-doc:: include/linux/hid.h
:doc: HID quirks
Quirks for USB devices can be specified while loading the usbhid module,
see ``modinfo usbhid``, although the proper fix should go into
hid-quirks.c and **be submitted upstream**.
See Documentation/process/submitting-patches.rst for guidelines on how
to submit a patch. Quirks for other busses need to go into hid-quirks.c.
Fixing HID report descriptors
-----------------------------
Should you need to patch HID report descriptors the easiest way is to
resort to eBPF, as described in Documentation/hid/hid-bpf.rst.
Basically, you can change any byte of the original HID report
descriptor. The examples in samples/hid should be a good starting point
for your code, see e.g. `samples/hid/hid_mouse.bpf.c`::
SEC("fmod_ret/hid_bpf_rdesc_fixup")
int BPF_PROG(hid_rdesc_fixup, struct hid_bpf_ctx *hctx)
{
....
data[39] = 0x31;
data[41] = 0x30;
return 0;
}
Of course this can be also done within the kernel source code, see e.g.
`drivers/hid/hid-aureal.c` or `drivers/hid/hid-samsung.c` for a slightly
more complex file.
Check Documentation/hid/hidreport-parsing.rst if you need any help
navigating the HID manuals and understanding the exact meaning of
the HID report descriptor hex numbers.
Whatever solution you come up with, please remember to **submit the
fix to the HID maintainers**, so that it can be directly integrated in
the kernel and that particular HID device will start working for
everyone else. See Documentation/process/submitting-patches.rst for
guidelines on how to do this.
Modifying the transmitted data on the fly
-----------------------------------------
Using eBPF it is also possible to modify the data exchanged with the
device. See again the examples in `samples/hid`.
Again, **please post your fix**, so that it can be integrated in the
kernel!
Writing a specialized driver
----------------------------
This should really be your last resort.
.. rubric:: Footnotes
.. [#hidraw] read hidraw: see Documentation/hid/hidraw.rst and
file `samples/hidraw/hid-example.c` for an example.
The output of ``hid-example`` would be, for the same mouse::
$ sudo ./hid-example
Report Descriptor Size: 52
Report Descriptor:
5 1 9 2 a1 1 9 1 a1 0 5 9 19 1 29 3 15 0 25 1 75 1 95 3 81 2 75 5 95 1 81 1 5 1 9 30 9 31 9 38 15 81 25 7f 75 8 95 3 81 6 c0 c0
Raw Name: PixArt USB Optical Mouse
Raw Phys: usb-0000:05:00.4-2.3/input0
Raw Info:
bustype: 3 (USB)
vendor: 0x093a
product: 0x2510
...
linux-7.2.3/Documentation/hid/hidraw.rst
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================================================================
HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices
================================================================
The hidraw driver provides a raw interface to USB and Bluetooth Human
Interface Devices (HIDs). It differs from hiddev in that reports sent and
received are not parsed by the HID parser, but are sent to and received from
the device unmodified.
Hidraw should be used if the userspace application knows exactly how to
communicate with the hardware device, and is able to construct the HID
reports manually. This is often the case when making userspace drivers for
custom HID devices.
Hidraw is also useful for communicating with non-conformant HID devices
which send and receive data in a way that is inconsistent with their report
descriptors. Because hiddev parses reports which are sent and received
through it, checking them against the device's report descriptor, such
communication with these non-conformant devices is impossible using hiddev.
Hidraw is the only alternative, short of writing a custom kernel driver, for
these non-conformant devices.
A benefit of hidraw is that its use by userspace applications is independent
of the underlying hardware type. Currently, hidraw is implemented for USB
and Bluetooth. In the future, as new hardware bus types are developed which
use the HID specification, hidraw will be expanded to add support for these
new bus types.
Hidraw uses a dynamic major number, meaning that udev should be relied on to
create hidraw device nodes. Udev will typically create the device nodes
directly under /dev (eg: /dev/hidraw0). As this location is distribution-
and udev rule-dependent, applications should use libudev to locate hidraw
devices attached to the system. There is a tutorial on libudev with a
working example at::
http://www.signal11.us/oss/udev/
https://web.archive.org/web/2019*/www.signal11.us
The HIDRAW API
---------------
read()
-------
read() will read a queued report received from the HID device. On USB
devices, the reports read using read() are the reports sent from the device
on the INTERRUPT IN endpoint. By default, read() will block until there is
a report available to be read. read() can be made non-blocking, by passing
the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using
fcntl().
On a device which uses numbered reports, the first byte of the returned data
will be the report number; the report data follows, beginning in the second
byte. For devices which do not use numbered reports, the report data
will begin at the first byte.
write()
-------
The write() function will write a report to the device. For USB devices, if
the device has an INTERRUPT OUT endpoint, the report will be sent on that
endpoint. If it does not, the report will be sent over the control endpoint,
using a SET_REPORT transfer.
The first byte of the buffer passed to write() should be set to the report
number. If the device does not use numbered reports, the first byte should
be set to 0. The report data itself should begin at the second byte.
ioctl()
-------
Hidraw supports the following ioctls:
HIDIOCGRDESCSIZE:
Get Report Descriptor Size
This ioctl will get the size of the device's report descriptor.
HIDIOCGRDESC:
Get Report Descriptor
This ioctl returns the device's report descriptor using a
hidraw_report_descriptor struct. Make sure to set the size field of the
hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.
HIDIOCGRAWINFO:
Get Raw Info
This ioctl will return a hidraw_devinfo struct containing the bus type, the
vendor ID (VID), and product ID (PID) of the device. The bus type can be one
of::
- BUS_USB
- BUS_HIL
- BUS_BLUETOOTH
- BUS_VIRTUAL
which are defined in uapi/linux/input.h.
HIDIOCGRAWNAME(len):
Get Raw Name
This ioctl returns a string containing the vendor and product strings of
the device. The returned string is Unicode, UTF-8 encoded.
HIDIOCGRAWPHYS(len):
Get Physical Address
This ioctl returns a string representing the physical address of the device.
For USB devices, the string contains the physical path to the device (the
USB controller, hubs, ports, etc). For Bluetooth devices, the string
contains the hardware (MAC) address of the device.
HIDIOCSFEATURE(len):
Send a Feature Report
This ioctl will send a feature report to the device. Per the HID
specification, feature reports are always sent using the control endpoint.
Set the first byte of the supplied buffer to the report number. For devices
which do not use numbered reports, set the first byte to 0. The report data
begins in the second byte. Make sure to set len accordingly, to one more
than the length of the report (to account for the report number).
HIDIOCGFEATURE(len):
Get a Feature Report
This ioctl will request a feature report from the device using the control
endpoint. The first byte of the supplied buffer should be set to the report
number of the requested report. For devices which do not use numbered
reports, set the first byte to 0. The returned report buffer will contain the
report number in the first byte, followed by the report data read from the
device. For devices which do not use numbered reports, the report data will
begin at the first byte of the returned buffer.
HIDIOCSINPUT(len):
Send an Input Report
This ioctl will send an input report to the device, using the control endpoint.
In most cases, setting an input HID report on a device is meaningless and has
no effect, but some devices may choose to use this to set or reset an initial
state of a report. The format of the buffer issued with this report is identical
to that of HIDIOCSFEATURE.
HIDIOCGINPUT(len):
Get an Input Report
This ioctl will request an input report from the device using the control
endpoint. This is slower on most devices where a dedicated In endpoint exists
for regular input reports, but allows the host to request the value of a
specific report number. Typically, this is used to request the initial states of
an input report of a device, before an application listens for normal reports via
the regular device read() interface. The format of the buffer issued with this report
is identical to that of HIDIOCGFEATURE.
HIDIOCSOUTPUT(len):
Send an Output Report
This ioctl will send an output report to the device, using the control endpoint.
This is slower on most devices where a dedicated Out endpoint exists for regular
output reports, but is added for completeness. Typically, this is used to set
the initial states of an output report of a device, before an application sends
updates via the regular device write() interface. The format of the buffer issued
with this report is identical to that of HIDIOCSFEATURE.
HIDIOCGOUTPUT(len):
Get an Output Report
This ioctl will request an output report from the device using the control
endpoint. Typically, this is used to retrieve the initial state of
an output report of a device, before an application updates it as necessary either
via a HIDIOCSOUTPUT request, or the regular device write() interface. The format
of the buffer issued with this report is identical to that of HIDIOCGFEATURE.
Example
-------
In samples/, find hid-example.c, which shows examples of read(), write(),
and all the ioctls for hidraw. The code may be used by anyone for any
purpose, and can serve as a starting point for developing applications using
hidraw.
Document by:
Alan Ott <alan@signal11.us>, Signal 11 Software
linux-7.2.3/Documentation/hid/hidreport-parsing.rst
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.. SPDX-License-Identifier: GPL-2.0
========================================
Manual parsing of HID report descriptors
========================================
Consider again the mouse HID report descriptor
introduced in Documentation/hid/hidintro.rst::
$ hexdump -C /sys/bus/hid/devices/0003\:093A\:2510.0002/report_descriptor
00000000 05 01 09 02 a1 01 09 01 a1 00 05 09 19 01 29 03 |..............).|
00000010 15 00 25 01 75 01 95 03 81 02 75 05 95 01 81 01 |..%.u.....u.....|
00000020 05 01 09 30 09 31 09 38 15 81 25 7f 75 08 95 03 |...0.1.8..%.u...|
00000030 81 06 c0 c0 |....|
00000034
and try to parse it by hand.
Start with the first number, 0x05: it carries 2 bits for the
length of the item, 2 bits for the type of the item and 4 bits for the
function::
+----------+
| 00000101 |
+----------+
^^
---- Length of data (see HID spec 6.2.2.2)
^^
------ Type of the item (see HID spec 6.2.2.2, then jump to 6.2.2.7)
^^^^
--------- Function of the item (see HID spec 6.2.2.7, then HUT Sec 3)
In our case, the length is 1 byte, the type is ``Global`` and the
function is ``Usage Page``, thus for parsing the value 0x01 in the second byte
we need to refer to HUT Sec 3.
The second number is the actual data, and its meaning can be found in
the HUT. We have a ``Usage Page``, thus we need to refer to HUT
Sec. 3, "Usage Pages"; from there, one sees that ``0x01`` stands for
``Generic Desktop Page``.
Moving now to the second two bytes, and following the same scheme,
``0x09`` (i.e. ``00001001``) will be followed by one byte (``01``)
and is a ``Local`` item (``10``). Thus, the meaning of the remaining four bits
(``0000``) is given in the HID spec Sec. 6.2.2.8 "Local Items", so that
we have a ``Usage``. From HUT, Sec. 4, "Generic Desktop Page", we see that
0x02 stands for ``Mouse``.
The following numbers can be parsed in the same way.
linux-7.2.3/Documentation/hid/index.rst
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.. SPDX-License-Identifier: GPL-2.0
=============================
Human Interface Devices (HID)
=============================
.. toctree::
:maxdepth: 1
hidintro
hiddev
hidraw
hid-sensor
hid-transport
hid-bpf
uhid
hid-alps
intel-ish-hid
intel-thc-hid
amd-sfh-hid
linux-7.2.3/Documentation/hid/intel-ish-hid.rst
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=================================
Intel Integrated Sensor Hub (ISH)
=================================
A sensor hub enables the ability to offload sensor polling and algorithm
processing to a dedicated low power co-processor. This allows the core
processor to go into low power modes more often, resulting in increased
battery life.
There are many vendors providing external sensor hubs conforming to HID
Sensor usage tables. These may be found in tablets, 2-in-1 convertible laptops
and embedded products. Linux has had this support since Linux 3.9.
Intel® introduced integrated sensor hubs as a part of the SoC starting from
Cherry Trail and now supported on multiple generations of CPU packages. There
are many commercial devices already shipped with Integrated Sensor Hubs (ISH).
These ISH also comply to HID sensor specification, but the difference is the
transport protocol used for communication. The current external sensor hubs
mainly use HID over I2C or USB. But ISH doesn't use either I2C or USB.
Overview
========
Using a analogy with a usbhid implementation, the ISH follows a similar model
for a very high speed communication::
----------------- ----------------------
| USB HID | --> | ISH HID |
----------------- ----------------------
----------------- ----------------------
| USB protocol | --> | ISH Transport |
----------------- ----------------------
----------------- ----------------------
| EHCI/XHCI | --> | ISH IPC |
----------------- ----------------------
PCI PCI
----------------- ----------------------
|Host controller| --> | ISH processor |
----------------- ----------------------
USB Link
----------------- ----------------------
| USB End points| --> | ISH Clients |
----------------- ----------------------
Like USB protocol provides a method for device enumeration, link management
and user data encapsulation, the ISH also provides similar services. But it is
very light weight tailored to manage and communicate with ISH client
applications implemented in the firmware.
The ISH allows multiple sensor management applications executing in the
firmware. Like USB endpoints the messaging can be to/from a client. As part of
enumeration process, these clients are identified. These clients can be simple
HID sensor applications, sensor calibration applications or sensor firmware
update applications.
The implementation model is similar, like USB bus, ISH transport is also
implemented as a bus. Each client application executing in the ISH processor
is registered as a device on this bus. The driver, which binds each device
(ISH HID driver) identifies the device type and registers with the HID core.
ISH Implementation: Block Diagram
=================================
::
---------------------------
| User Space Applications |
---------------------------
----------------IIO ABI----------------
--------------------------
| IIO Sensor Drivers |
--------------------------
--------------------------
| IIO core |
--------------------------
--------------------------
| HID Sensor Hub MFD |
--------------------------
--------------------------
| HID Core |
--------------------------
--------------------------
| HID over ISH Client |
--------------------------
--------------------------
| ISH Transport (ISHTP) |
--------------------------
--------------------------
| IPC Drivers |
--------------------------
OS
---------------- PCI -----------------
Hardware + Firmware
----------------------------
| ISH Hardware/Firmware(FW) |
----------------------------
High level processing in above blocks
=====================================
Hardware Interface
------------------
The ISH is exposed as "Non-VGA unclassified PCI device" to the host. The PCI
product and vendor IDs are changed from different generations of processors. So
the source code which enumerates drivers needs to update from generation to
generation.
Inter Processor Communication (IPC) driver
------------------------------------------
Location: drivers/hid/intel-ish-hid/ipc
The IPC message uses memory mapped I/O. The registers are defined in
hw-ish-regs.h.
IPC/FW message types
^^^^^^^^^^^^^^^^^^^^
There are two types of messages, one for management of link and another for
messages to and from transport layers.
TX and RX of Transport messages
...............................
A set of memory mapped register offers support of multi-byte messages TX and
RX (e.g. IPC_REG_ISH2HOST_MSG, IPC_REG_HOST2ISH_MSG). The IPC layer maintains
internal queues to sequence messages and send them in order to the firmware.
Optionally the caller can register handler to get notification of completion.
A doorbell mechanism is used in messaging to trigger processing in host and
client firmware side. When ISH interrupt handler is called, the ISH2HOST
doorbell register is used by host drivers to determine that the interrupt
is for ISH.
Each side has 32 32-bit message registers and a 32-bit doorbell. Doorbell
register has the following format::
Bits 0..6: fragment length (7 bits are used)
Bits 10..13: encapsulated protocol
Bits 16..19: management command (for IPC management protocol)
Bit 31: doorbell trigger (signal H/W interrupt to the other side)
Other bits are reserved, should be 0.
Transport layer interface
^^^^^^^^^^^^^^^^^^^^^^^^^
To abstract HW level IPC communication, a set of callbacks is registered.
The transport layer uses them to send and receive messages.
Refer to struct ishtp_hw_ops for callbacks.
ISH Transport layer
-------------------
Location: drivers/hid/intel-ish-hid/ishtp/
A Generic Transport Layer
^^^^^^^^^^^^^^^^^^^^^^^^^
The transport layer is a bi-directional protocol, which defines:
- Set of commands to start, stop, connect, disconnect and flow control
(see ishtp/hbm.h for details)
- A flow control mechanism to avoid buffer overflows
This protocol resembles bus messages described in the following document:
http://www.intel.com/content/dam/www/public/us/en/documents/technical-specifications/dcmi-hi-1-0-spec.pdf
"Chapter 7: Bus Message Layer".
Connection and Flow Control Mechanism
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Each FW client and a protocol is identified by a UUID. In order to communicate
to a FW client, a connection must be established using connect request and
response bus messages. If successful, a pair (host_client_id and fw_client_id)
will identify the connection.
Once connection is established, peers send each other flow control bus messages
independently. Every peer may send a message only if it has received a
flow-control credit before. Once it has sent a message, it may not send another one
before receiving the next flow control credit.
Either side can send disconnect request bus message to end communication. Also
the link will be dropped if major FW reset occurs.
Peer to Peer data transfer
^^^^^^^^^^^^^^^^^^^^^^^^^^
Peer to Peer data transfer can happen with or without using DMA. Depending on
the sensor bandwidth requirement DMA can be enabled by using module parameter
ishtp_use_dma under intel_ishtp.
Each side (host and FW) manages its DMA transfer memory independently. When an
ISHTP client from either host or FW side wants to send something, it decides
whether to send over IPC or over DMA; for each transfer the decision is
independent. The sending side sends DMA_XFER message when the message is in
the respective host buffer (TX when host client sends, RX when FW client
sends). The recipient of DMA message responds with DMA_XFER_ACK, indicating
the sender that the memory region for that message may be reused.
DMA initialization is started with host sending DMA_ALLOC_NOTIFY bus message
(that includes RX buffer) and FW responds with DMA_ALLOC_NOTIFY_ACK.
Additionally to DMA address communication, this sequence checks capabilities:
if the host doesn't support DMA, then it won't send DMA allocation, so FW can't
send DMA; if FW doesn't support DMA then it won't respond with
DMA_ALLOC_NOTIFY_ACK, in which case host will not use DMA transfers.
Here ISH acts as busmaster DMA controller. Hence when host sends DMA_XFER,
it's request to do host->ISH DMA transfer; when FW sends DMA_XFER, it means
that it already did DMA and the message resides at host. Thus, DMA_XFER
and DMA_XFER_ACK act as ownership indicators.
At initial state all outgoing memory belongs to the sender (TX to host, RX to
FW), DMA_XFER transfers ownership on the region that contains ISHTP message to
the receiving side, DMA_XFER_ACK returns ownership to the sender. A sender
need not wait for previous DMA_XFER to be ack'ed, and may send another message
as long as remaining continuous memory in its ownership is enough.
In principle, multiple DMA_XFER and DMA_XFER_ACK messages may be sent at once
(up to IPC MTU), thus allowing for interrupt throttling.
Currently, ISH FW decides to send over DMA if ISHTP message is more than 3 IPC
fragments and via IPC otherwise.
Ring Buffers
^^^^^^^^^^^^
When a client initiates a connection, a ring of RX and TX buffers is allocated.
The size of ring can be specified by the client. HID client sets 16 and 32 for
TX and RX buffers respectively. On send request from client, the data to be
sent is copied to one of the send ring buffer and scheduled to be sent using
bus message protocol. These buffers are required because the FW may have not
have processed the last message and may not have enough flow control credits
to send. Same thing holds true on receive side and flow control is required.
Host Enumeration
^^^^^^^^^^^^^^^^
The host enumeration bus command allows discovery of clients present in the FW.
There can be multiple sensor clients and clients for calibration function.
To ease implementation and allow independent drivers to handle each client,
this transport layer takes advantage of Linux Bus driver model. Each
client is registered as device on the transport bus (ishtp bus).
Enumeration sequence of messages:
- Host sends HOST_START_REQ_CMD, indicating that host ISHTP layer is up.
- FW responds with HOST_START_RES_CMD
- Host sends HOST_ENUM_REQ_CMD (enumerate FW clients)
- FW responds with HOST_ENUM_RES_CMD that includes bitmap of available FW
client IDs
- For each FW ID found in that bitmap host sends
HOST_CLIENT_PROPERTIES_REQ_CMD
- FW responds with HOST_CLIENT_PROPERTIES_RES_CMD. Properties include UUID,
max ISHTP message size, etc.
- Once host received properties for that last discovered client, it considers
ISHTP device fully functional (and allocates DMA buffers)
HID over ISH Client
-------------------
Location: drivers/hid/intel-ish-hid
The ISHTP client driver is responsible for:
- enumerate HID devices under FW ISH client
- Get Report descriptor
- Register with HID core as a LL driver
- Process Get/Set feature request
- Get input reports
HID Sensor Hub MFD and IIO sensor drivers
-----------------------------------------
The functionality in these drivers is the same as an external sensor hub.
Refer to
Documentation/hid/hid-sensor.rst for HID sensor
Documentation/ABI/testing/sysfs-bus-iio for IIO ABIs to user space.
End to End HID transport Sequence Diagram
-----------------------------------------
::
HID-ISH-CLN ISHTP IPC HW
| | | |
| | |-----WAKE UP------------------>|
| | | |
| | |-----HOST READY--------------->|
| | | |
| | |<----MNG_RESET_NOTIFY_ACK----- |
| | | |
| |<----ISHTP_START------ | |
| | | |
| |<-----------------HOST_START_RES_CMD-------------------|
| | | |
| |------------------QUERY_SUBSCRIBER-------------------->|
| | | |
| |------------------HOST_ENUM_REQ_CMD------------------->|
| | | |
| |<-----------------HOST_ENUM_RES_CMD--------------------|
| | | |
| |------------------HOST_CLIENT_PROPERTIES_REQ_CMD------>|
| | | |
| |<-----------------HOST_CLIENT_PROPERTIES_RES_CMD-------|
| Create new device on in ishtp bus | |
| | | |
| |------------------HOST_CLIENT_PROPERTIES_REQ_CMD------>|
| | | |
| |<-----------------HOST_CLIENT_PROPERTIES_RES_CMD-------|
| Create new device on in ishtp bus | |
| | | |
| |--Repeat HOST_CLIENT_PROPERTIES_REQ_CMD-till last one--|
| | | |
probed()
|----ishtp_cl_connect--->|----------------- CLIENT_CONNECT_REQ_CMD-------------->|
| | | |
| |<----------------CLIENT_CONNECT_RES_CMD----------------|
| | | |
|register event callback | | |
| | | |
|ishtp_cl_send(
HOSTIF_DM_ENUM_DEVICES) |----------fill ishtp_msg_hdr struct write to HW----- >|
| | | |
| | |<-----IRQ(IPC_PROTOCOL_ISHTP---|
| | | |
|<--ENUM_DEVICE RSP------| | |
| | | |
for each enumerated device
|ishtp_cl_send(
HOSTIF_GET_HID_DESCRIPTOR|----------fill ishtp_msg_hdr struct write to HW----- >|
| | | |
...Response
| | | |
for each enumerated device
|ishtp_cl_send(
HOSTIF_GET_REPORT_DESCRIPTOR|--------------fill ishtp_msg_hdr struct write to HW-- >|
| | | |
| | | |
hid_allocate_device
| | | |
hid_add_device | | |
| | | |
ISH Firmware Loading from Host Flow
-----------------------------------
Starting from the Lunar Lake generation, the ISH firmware has been divided into two components for better space optimization and increased flexibility. These components include a bootloader that is integrated into the BIOS, and a main firmware that is stored within the operating system's file system.
The process works as follows:
- Initially, the ISHTP driver sends a command, HOST_START_REQ_CMD, to the ISH bootloader. In response, the bootloader sends back a HOST_START_RES_CMD. This response includes the ISHTP_SUPPORT_CAP_LOADER bit. Subsequently, the ISHTP driver checks if this bit is set. If it is, the firmware loading process from the host begins.
- During this process, the ISHTP driver first invokes the request_firmware() function, followed by sending a LOADER_CMD_XFER_QUERY command. Upon receiving a response from the bootloader, the ISHTP driver sends a LOADER_CMD_XFER_FRAGMENT command. After receiving another response, the ISHTP driver sends a LOADER_CMD_START command. The bootloader responds and then proceeds to the Main Firmware.
- After the process concludes, the ISHTP driver calls the release_firmware() function.
For more detailed information, please refer to the flow descriptions provided below:
::
+---------------+ +-----------------+
| ISHTP Driver | | ISH Bootloader |
+---------------+ +-----------------+
| |
|~~~Send HOST_START_REQ_CMD~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>|
| |
|<--Send HOST_START_RES_CMD(Includes ISHTP_SUPPORT_CAP_LOADER bit)----|
| |
****************************************************************************************
* if ISHTP_SUPPORT_CAP_LOADER bit is set *
****************************************************************************************
| |
|~~~start loading firmware from host process~~~+ |
| | |
|<---------------------------------------------+ |
| |
--------------------------- |
| Call request_firmware() | |
--------------------------- |
| |
|~~~Send LOADER_CMD_XFER_QUERY~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>|
| |
|<--Send response-----------------------------------------------------|
| |
|~~~Send LOADER_CMD_XFER_FRAGMENT~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>|
| |
|<--Send response-----------------------------------------------------|
| |
|~~~Send LOADER_CMD_START~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>|
| |
|<--Send response-----------------------------------------------------|
| |
| |~~~Jump to Main Firmware~~~+
| | |
| |<--------------------------+
| |
--------------------------- |
| Call release_firmware() | |
--------------------------- |
| |
****************************************************************************************
* end if *
****************************************************************************************
| |
+---------------+ +-----------------+
| ISHTP Driver | | ISH Bootloader |
+---------------+ +-----------------+
Vendor Custom Firmware Loading
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The firmware running inside ISH can be provided by Intel or developed by vendors using the Firmware Development Kit (FDK) provided by Intel.
Intel will upstream the Intel-built firmware to the ``linux-firmware.git`` repository, located under the path ``intel/ish/``. For the Lunar Lake platform, the Intel-built ISH firmware will be named ``ish_lnlm.bin``.
Vendors who wish to upstream their custom firmware should follow these guidelines for naming their firmware files:
- The firmware filename should use one of the following patterns:
- ``ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_FAMILY_CRC32}_${PRODUCT_NAME_CRC32}_${PRODUCT_SKU_CRC32}.bin``
- ``ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_FAMILY_CRC32}_${PRODUCT_SKU_CRC32}.bin``
- ``ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_FAMILY_CRC32}_${PRODUCT_NAME_CRC32}.bin``
- ``ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_FAMILY_CRC32}.bin``
- ``ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_NAME_CRC32}_${PRODUCT_SKU_CRC32}.bin``
- ``ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_SKU_CRC32}.bin``
- ``ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_NAME_CRC32}.bin``
- ``ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}.bin``
- ``${intel_plat_gen}`` indicates the Intel platform generation (e.g., ``lnlm`` for Lunar Lake) and must not exceed 8 characters in length.
- ``${SYS_VENDOR_CRC32}`` is the CRC32 checksum of the ``sys_vendor`` value from the DMI field ``DMI_SYS_VENDOR``.
- ``${PRODUCT_FAMILY_CRC32}`` is the CRC32 checksum of the ``product_family`` value from the DMI field ``DMI_PRODUCT_FAMILY``.
- ``${PRODUCT_NAME_CRC32}`` is the CRC32 checksum of the ``product_name`` value from the DMI field ``DMI_PRODUCT_NAME``.
- ``${PRODUCT_SKU_CRC32}`` is the CRC32 checksum of the ``product_sku`` value from the DMI field ``DMI_PRODUCT_SKU``.
During system boot, the ISH Linux driver will attempt to load the firmware in the following order, prioritizing custom firmware with more precise matching patterns:
1. ``intel/ish/ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_FAMILY_CRC32}_${PRODUCT_NAME_CRC32}_${PRODUCT_SKU_CRC32}.bin``
2. ``intel/ish/ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_FAMILY_CRC32}_${PRODUCT_SKU_CRC32}.bin``
3. ``intel/ish/ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_FAMILY_CRC32}_${PRODUCT_NAME_CRC32}.bin``
4. ``intel/ish/ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_FAMILY_CRC32}.bin``
5. ``intel/ish/ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_NAME_CRC32}_${PRODUCT_SKU_CRC32}.bin``
6. ``intel/ish/ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_SKU_CRC32}.bin``
7. ``intel/ish/ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}_${PRODUCT_NAME_CRC32}.bin``
8. ``intel/ish/ish_${intel_plat_gen}_${SYS_VENDOR_CRC32}.bin``
9. ``intel/ish/ish_${intel_plat_gen}.bin``
The driver will load the first matching firmware and skip the rest. If no matching firmware is found, it will proceed to the next pattern in the specified order. If all searches fail, the default Intel firmware, listed last in the order above, will be loaded.
ISH Debugging
-------------
To debug ISH, event tracing mechanism is used. To enable debug logs::
echo 1 > /sys/kernel/tracing/events/intel_ish/enable
cat /sys/kernel/tracing/trace
ISH IIO sysfs Example on Lenovo thinkpad Yoga 260
-------------------------------------------------
::
root@otcpl-ThinkPad-Yoga-260:~# tree -l /sys/bus/iio/devices/
/sys/bus/iio/devices/
├── iio:device0 -> ../../../devices/0044:8086:22D8.0001/HID-SENSOR-200073.9.auto/iio:device0
│   ├── buffer
│   │   ├── enable
│   │   ├── length
│   │   └── watermark
...
│   ├── in_accel_hysteresis
│   ├── in_accel_offset
│   ├── in_accel_sampling_frequency
│   ├── in_accel_scale
│   ├── in_accel_x_raw
│   ├── in_accel_y_raw
│   ├── in_accel_z_raw
│   ├── name
│   ├── scan_elements
│   │   ├── in_accel_x_en
│   │   ├── in_accel_x_index
│   │   ├── in_accel_x_type
│   │   ├── in_accel_y_en
│   │   ├── in_accel_y_index
│   │   ├── in_accel_y_type
│   │   ├── in_accel_z_en
│   │   ├── in_accel_z_index
│   │   └── in_accel_z_type
...
│   │   ├── devices
│   │   │   │   ├── buffer
│   │   │   │   │   ├── enable
│   │   │   │   │   ├── length
│   │   │   │   │   └── watermark
│   │   │   │   ├── dev
│   │   │   │   ├── in_intensity_both_raw
│   │   │   │   ├── in_intensity_hysteresis
│   │   │   │   ├── in_intensity_offset
│   │   │   │   ├── in_intensity_sampling_frequency
│   │   │   │   ├── in_intensity_scale
│   │   │   │   ├── name
│   │   │   │   ├── scan_elements
│   │   │   │   │   ├── in_intensity_both_en
│   │   │   │   │   ├── in_intensity_both_index
│   │   │   │   │   └── in_intensity_both_type
│   │   │   │   ├── trigger
│   │   │   │   │   └── current_trigger
...
│   │   │   │   ├── buffer
│   │   │   │   │   ├── enable
│   │   │   │   │   ├── length
│   │   │   │   │   └── watermark
│   │   │   │   ├── dev
│   │   │   │   ├── in_magn_hysteresis
│   │   │   │   ├── in_magn_offset
│   │   │   │   ├── in_magn_sampling_frequency
│   │   │   │   ├── in_magn_scale
│   │   │   │   ├── in_magn_x_raw
│   │   │   │   ├── in_magn_y_raw
│   │   │   │   ├── in_magn_z_raw
│   │   │   │   ├── in_rot_from_north_magnetic_tilt_comp_raw
│   │   │   │   ├── in_rot_hysteresis
│   │   │   │   ├── in_rot_offset
│   │   │   │   ├── in_rot_sampling_frequency
│   │   │   │   ├── in_rot_scale
│   │   │   │   ├── name
...
│   │   │   │   ├── scan_elements
│   │   │   │   │   ├── in_magn_x_en
│   │   │   │   │   ├── in_magn_x_index
│   │   │   │   │   ├── in_magn_x_type
│   │   │   │   │   ├── in_magn_y_en
│   │   │   │   │   ├── in_magn_y_index
│   │   │   │   │   ├── in_magn_y_type
│   │   │   │   │   ├── in_magn_z_en
│   │   │   │   │   ├── in_magn_z_index
│   │   │   │   │   ├── in_magn_z_type
│   │   │   │   │   ├── in_rot_from_north_magnetic_tilt_comp_en
│   │   │   │   │   ├── in_rot_from_north_magnetic_tilt_comp_index
│   │   │   │   │   └── in_rot_from_north_magnetic_tilt_comp_type
│   │   │   │   ├── trigger
│   │   │   │   │   └── current_trigger
...
│   │   │   │   ├── buffer
│   │   │   │   │   ├── enable
│   │   │   │   │   ├── length
│   │   │   │   │   └── watermark
│   │   │   │   ├── dev
│   │   │   │   ├── in_anglvel_hysteresis
│   │   │   │   ├── in_anglvel_offset
│   │   │   │   ├── in_anglvel_sampling_frequency
│   │   │   │   ├── in_anglvel_scale
│   │   │   │   ├── in_anglvel_x_raw
│   │   │   │   ├── in_anglvel_y_raw
│   │   │   │   ├── in_anglvel_z_raw
│   │   │   │   ├── name
│   │   │   │   ├── scan_elements
│   │   │   │   │   ├── in_anglvel_x_en
│   │   │   │   │   ├── in_anglvel_x_index
│   │   │   │   │   ├── in_anglvel_x_type
│   │   │   │   │   ├── in_anglvel_y_en
│   │   │   │   │   ├── in_anglvel_y_index
│   │   │   │   │   ├── in_anglvel_y_type
│   │   │   │   │   ├── in_anglvel_z_en
│   │   │   │   │   ├── in_anglvel_z_index
│   │   │   │   │   └── in_anglvel_z_type
│   │   │   │   ├── trigger
│   │   │   │   │   └── current_trigger
...
│   │   │   │   ├── buffer
│   │   │   │   │   ├── enable
│   │   │   │   │   ├── length
│   │   │   │   │   └── watermark
│   │   │   │   ├── dev
│   │   │   │   ├── in_anglvel_hysteresis
│   │   │   │   ├── in_anglvel_offset
│   │   │   │   ├── in_anglvel_sampling_frequency
│   │   │   │   ├── in_anglvel_scale
│   │   │   │   ├── in_anglvel_x_raw
│   │   │   │   ├── in_anglvel_y_raw
│   │   │   │   ├── in_anglvel_z_raw
│   │   │   │   ├── name
│   │   │   │   ├── scan_elements
│   │   │   │   │   ├── in_anglvel_x_en
│   │   │   │   │   ├── in_anglvel_x_index
│   │   │   │   │   ├── in_anglvel_x_type
│   │   │   │   │   ├── in_anglvel_y_en
│   │   │   │   │   ├── in_anglvel_y_index
│   │   │   │   │   ├── in_anglvel_y_type
│   │   │   │   │   ├── in_anglvel_z_en
│   │   │   │   │   ├── in_anglvel_z_index
│   │   │   │   │   └── in_anglvel_z_type
│   │   │   │   ├── trigger
│   │   │   │   │   └── current_trigger
...
linux-7.2.3/Documentation/hid/intel-thc-hid.rst
+596
View File
@@ -0,0 +1,596 @@
.. SPDX-License-Identifier: GPL-2.0
=================================
Intel Touch Host Controller (THC)
=================================
Touch Host Controller is the name of the IP block in PCH that interface with Touch Devices (ex:
touchscreen, touchpad etc.). It is comprised of 3 key functional blocks:
- A natively half-duplex Quad I/O capable SPI master
- Low latency I2C interface to support HIDI2C compliant devices
- A HW sequencer with RW DMA capability to system memory
It has a single root space IOSF Primary interface that supports transactions to/from touch devices.
Host driver configures and controls the touch devices over THC interface. THC provides high
bandwidth DMA services to the touch driver and transfers the HID report to host system main memory.
Hardware sequencer within the THC is responsible for transferring (via DMA) data from touch devices
into system memory. A ring buffer is used to avoid data loss due to asynchronous nature of data
consumption (by host) in relation to data production (by touch device via DMA).
Unlike other common SPI/I2C controllers, THC handles the HID device data interrupt and reset
signals directly.
1. Overview
===========
1.1 THC software/hardware stack
-------------------------------
Below diagram illustrates the high-level architecture of THC software/hardware stack, which is fully
capable of supporting HIDSPI/HIDI2C protocol in Linux OS.
::
----------------------------------------------
| +-----------------------------------+ |
| | Input Device | |
| +-----------------------------------+ |
| +-----------------------------------+ |
| | HID Multi-touch Driver | |
| +-----------------------------------+ |
| +-----------------------------------+ |
| | HID Core | |
| +-----------------------------------+ |
| +-----------------------------------+ |
| | THC QuickSPI/QuickI2C Driver | |
| +-----------------------------------+ |
| +-----------------------------------+ |
| | THC Hardware Driver | |
| +-----------------------------------+ |
| +----------------+ +----------------+ |
| SW | PCI Bus Driver | | ACPI Resource | |
| +----------------+ +----------------+ |
----------------------------------------------
----------------------------------------------
| +-----------------------------------+ |
| HW | PCI Bus | |
| +-----------------------------------+ |
| +-----------------------------------+ |
| | THC Controller | |
| +-----------------------------------+ |
| +-----------------------------------+ |
| | Touch IC | |
| +-----------------------------------+ |
----------------------------------------------
Touch IC (TIC), also as known as the Touch devices (touchscreen or touchpad). The discrete analog
components that sense and transfer either discrete touch data or heatmap data in the form of HID
reports over the SPI/I2C bus to the THC Controller on the host.
THC Host Controller, which is a PCI device HBA (host bus adapter), integrated into the PCH, that
serves as a bridge between the Touch ICs and the host.
THC Hardware Driver, provides THC hardware operation APIs for above QuickSPI/QuickI2C driver, it
accesses THC MMIO registers to configure and control THC hardware.
THC QuickSPI/QuickI2C driver, also as known as HIDSPI/HIDI2C driver, is registered as a HID
low-level driver that manages the THC Controller and implements HIDSPI/HIDI2C protocol.
1.2 THC hardware diagram
------------------------
Below diagram shows THC hardware components::
---------------------------------
| THC Controller |
| +---------------------------+ |
| | PCI Config Space | |
| +---------------------------+ |
| +---------------------------+ |
| + MMIO Registers | |
| +---------------------------+ |
+---------------+ | +------------+ +------------+ |
| System Memory +---+--+ DMA | | PIO | |
+---------------+ | +------------+ +------------+ |
| +---------------------------+ |
| | HW Sequencer | |
| +---------------------------+ |
| +------------+ +------------+ |
| | SPI/I2C | | GPIO | |
| | Controller | | Controller | |
| +------------+ +------------+ |
---------------------------------
As THC is exposed as a PCI devices, so it has standard PCI config space registers for PCI
enumeration and configuration.
MMIO Registers, which provide registers access for driver to configure and control THC hardware,
the registers include several categories: Interrupt status and control, DMA configure,
PIO (Programmed I/O, defined in section 3.2) status and control, SPI bus configure, I2C subIP
status and control, reset status and control...
THC provides two ways for driver to communicate with external Touch ICs: PIO and DMA.
PIO can let driver manually write/read data to/from Touch ICs, instead, THC DMA can
automatically write/read data without driver involved.
HW Sequencer includes THC major logic, it gets instruction from MMIO registers to control
SPI bus and I2C bus to finish a bus data transaction, it also can automatically handle
Touch ICs interrupt and start DMA receive/send data from/to Touch ICs according to interrupt
type. That means THC HW Sequencer understands HIDSPI/HIDI2C transfer protocol, and handle
the communication without driver involved, what driver needs to do is just configure the THC
properly, and prepare the formatted data packet or handle received data packet.
As THC supports HIDSPI/HIDI2C protocols, it has SPI controller and I2C subIP in it to expose
SPI bus and I2C bus. THC also integrates a GPIO controller to provide interrupt line support
and reset line support.
2. THC Hardware Interface
=========================
2.1 Host Interface
------------------
THC is exposed as "PCI Digitizer device" to the host. The PCI product and device IDs are
changed from different generations of processors. So the source code which enumerates drivers
needs to update from generation to generation.
2.2 Device Interface
--------------------
THC supports two types of bus for Touch IC connection: Enhanced SPI bus and I2C bus.
2.2.1 SPI Port
~~~~~~~~~~~~~~
When PORT_TYPE = 00b in MMIO registers, THC uses SPI interfaces to communicate with external
Touch IC. THC enhanced SPI Bus supports different SPI modes: standard Single IO mode,
Dual IO mode and Quad IO mode.
In Single IO mode, THC drives MOSI line to send data to Touch ICs, and receives data from Touch
ICs data from MISO line. In Dual IO mode, THC drivers MOSI and MISO both for data sending, and
also receives the data on both line. In Quad IO mode, there are other two lines (IO2 and IO3)
are added, THC drives MOSI (IO0), MISO (IO1), IO2 and IO3 at the same time for data sending, and
also receives the data on those 4 lines. Driver needs to configure THC in different mode by
setting different opcode.
Beside IO mode, driver also needs to configure SPI bus speed. THC supports up to 42MHz SPI clock
on Intel Lunar Lake platform.
For THC sending data to Touch IC, the data flow on SPI bus::
| --------------------THC sends---------------------------------|
<8Bits OPCode><24Bits Slave Address><Data><Data><Data>...........
For THC receiving data from Touch IC, the data flow on SPI bus::
| ---------THC Sends---------------||-----Touch IC sends--------|
<8Bits OPCode><24Bits Slave Address><Data><Data><Data>...........
2.2.2 I2C Port
~~~~~~~~~~~~~~
THC also integrates I2C controller in it, it's called I2C SubSystem. When PORT_TYPE = 01, THC
is configured to I2C mode. Comparing to SPI mode which can be configured through MMIO registers
directly, THC needs to use PIO read (by setting SubIP read opcode) to I2C subIP APB registers'
value and use PIO write (by setting SubIP write opcode) to do a write operation.
2.2.3 GPIO interface
~~~~~~~~~~~~~~~~~~~~
THC also includes two GPIO pins, one for interrupt and the other for device reset control.
Interrupt line can be configured to either level triggered or edge triggered by setting MMIO
Control register.
Reset line is controlled by BIOS (or EFI) through ACPI _RST method, driver needs to call this
device ACPI _RST method to reset touch IC during initialization.
2.3 Max input size control
--------------------------
This is a new feature introduced in Panther Lake platform, THC hardware allows driver to set
a max input size for RxDMA. After this max size gets set and enabled, for every input report
packet reading, THC hardware sequencer will first read incoming input packet size, then compare
input packet size with the given max size:
- if input packet size <= max size, THC continues using input packet size to finish the reading
- if input packet size > max size, there is potential input data crash risk during
transferring, THC will use max size instead of input packet size for reading
This feature is used to avoid data corruption which will cause RxDMA buffer overrun issue for
I2C bus, and enhance whole system stability.
2.4 Interrupt delay
-------------------
Because of MCU performance limitation, some touch devices cannot de-assert interrupt pin
immediately after input data is transferred, which cause an interrupt toggle delay. But THC
always detects next interrupt immediately after last input interrupt is handled. In this
case, the delayed interrupt de-assertion will be recognized as a new interrupt signal by THC,
and causes THC to start an input report reading spuriously.
In order to avoid this situation, THC introduced interrupt delay new feature in Panther Lake
platform, where THC allows driver to set an interrupt delay. After this feature is enabled,
THC will delay this given time for next interrupt detection.
3. High level concept
=====================
3.1 Opcode
----------
Opcode (operation code) is used to tell THC or Touch IC what the operation will be, such as PIO
read or PIO write.
When THC is configured to SPI mode, opcodes are used for determining the read/write IO mode.
There are some OPCode examples for SPI IO mode:
======= ==============================
opcode Corresponding SPI command
======= ==============================
0x0B Read Single I/O
0x02 Write Single I/O
0xBB Read Dual I/O
0xB2 Write Dual I/O
0xEB Read Quad I/O
0xE2 Write Quad I/O
======= ==============================
In general, different touch IC has different OPCode definition. According to HIDSPI
protocol whitepaper, those OPCodes are defined in device ACPI table, and driver needs to
query those information through OS ACPI APIs during driver initialization, then configures
THC MMIO OPCode registers with correct setting.
When THC is working in I2C mode, opcodes are used to tell THC what's the next PIO type:
I2C SubIP APB register read, I2C SubIP APB register write, I2C touch IC device read,
I2C touch IC device write, I2C touch IC device write followed by read.
Here are the THC pre-defined opcodes for I2C mode:
======= =================================================== ===========
opcode Corresponding I2C command Address
======= =================================================== ===========
0x12 Read I2C SubIP APB internal registers 0h - FFh
0x13 Write I2C SubIP APB internal registers 0h - FFh
0x14 Read external Touch IC through I2C bus N/A
0x18 Write external Touch IC through I2C bus N/A
0x1C Write then read external Touch IC through I2C bus N/A
======= =================================================== ===========
3.2 PIO
-------
THC provides a programmed I/O (PIO) access interface for the driver to access the touch IC's
configuration registers, or access I2C subIP's configuration registers. To use PIO to perform
I/O operations, driver should pre-program PIO control registers and PIO data registers and kick
off the sequencing cycle. THC uses different PIO opcodes to distinguish different PIO
operations (PIO read/write/write followed by read).
If there is a Sequencing Cycle In Progress and an attempt is made to program any of the control,
address, or data register the cycle is blocked and a sequence error will be encountered.
A status bit indicates when the cycle has completed allowing the driver to know when read results
can be checked and/or when to initiate a new command. If enabled, the cycle done assertion can
interrupt driver with an interrupt.
Because THC only has 16 FIFO registers for PIO, so all the data transfer through PIO shouldn't
exceed 64 bytes.
As DMA needs max packet size for transferring configuration, and the max packet size information
always in HID device descriptor which needs THC driver to read it out from HID Device (Touch IC).
So PIO typical use case is, before DMA initialization, write RESET command (PIO write), read
RESET response (PIO read or PIO write followed by read), write Power ON command (PIO write), read
device descriptor (PIO read).
For how to issue a PIO operation, here is the steps which driver needs follow:
- Program read/write data size in THC_SS_BC.
- Program I/O target address in THC_SW_SEQ_DATA0_ADDR.
- If write, program the write data in THC_SW_SEQ_DATA0..THC_SW_SEQ_DATAn.
- Program the PIO opcode in THC_SS_CMD.
- Set TSSGO = 1 to start the PIO write sequence.
- If THC_SS_CD_IE = 1, SW will receives a MSI when the PIO is completed.
- If read, read out the data in THC_SW_SEQ_DATA0..THC_SW_SEQ_DATAn.
3.3 DMA
-------
THC has 4 DMA channels: Read DMA1, Read DMA2, Write DMA and Software DMA.
3.3.1 Read DMA Channel
~~~~~~~~~~~~~~~~~~~~~~
THC has two Read DMA engines: 1st RxDMA (RxDMA1) and 2nd RxDMA (RxDMA2). RxDMA1 is reserved for
raw data mode. RxDMA2 is used for HID data mode and it is the RxDMA engine currently driver uses
for HID input report data retrieval.
RxDMA's typical use case is auto receiving the data from Touch IC. Once RxDMA is enabled by
software, THC will start auto-handling receiving logic.
For SPI mode, THC RxDMA sequence is: when Touch IC triggers a interrupt to THC, THC reads out
report header to identify what's the report type, and what's the report length, according to
above information, THC reads out report body to internal FIFO and start RxDMA coping the data
to system memory. After that, THC update interrupt cause register with report type, and update
RxDMA PRD table read pointer, then trigger a MSI interrupt to notify driver RxDMA finishing
data receiving.
For I2C mode, THC RxDMA's behavior is a little bit different, because of HIDI2C protocol difference
with HIDSPI protocol, RxDMA only be used to receive input report. The sequence is, when Touch IC
triggers a interrupt to THC, THC first reads out 2 bytes from input report address to determine the
packet length, then use this packet length to start a DMA reading from input report address for
input report data. After that, THC update RxDMA PRD table read pointer, then trigger a MSI interrupt
to notify driver input report data is ready in system memory.
All above sequence is hardware automatically handled, all driver needs to do is configure RxDMA and
waiting for interrupt ready then read out the data from system memory.
3.3.2 Software DMA channel
~~~~~~~~~~~~~~~~~~~~~~~~~~
THC supports a software triggered RxDMA mode to read the touch data from touch IC. This SW RxDMA
is the 3rd THC RxDMA engine with the similar functionalities as the existing two RxDMAs, the only
difference is this SW RxDMA is triggered by software, and RxDMA2 is triggered by external Touch IC
interrupt. It gives a flexibility to software driver to use RxDMA read Touch IC data in any time.
Before software starts a SW RxDMA, it shall stop the 1st and 2nd RxDMA, clear PRD read/write pointer
and quiesce the device interrupt (THC_DEVINT_QUIESCE_HW_STS = 1), other operations are the same with
RxDMA.
3.3.3 Write DMA Channel
~~~~~~~~~~~~~~~~~~~~~~~
THC has one write DMA engine, which can be used for sending data to Touch IC automatically.
According to HIDSPI and HIDI2C protocol, every time only one command can be sent to touch IC, and
before last command is completely handled, next command cannot be sent, THC write DMA engine only
supports single PRD table.
What driver needs to do is, preparing PRD table and DMA buffer, then copy data to DMA buffer and
update PRD table with buffer address and buffer length, then start write DMA. THC will
automatically send the data to touch IC, and trigger a DMA completion interrupt once transferring
is done.
3.4 PRD
-------
Physical Region Descriptor (PRD) provides the memory mapping description for THC DMAs.
3.4.1 PRD table and entry
~~~~~~~~~~~~~~~~~~~~~~~~~
In order to improve physical DMA memory usage, modern drivers trend to allocate a virtually
contiguous, but physically fragmented buffer of memory for each data buffer. Linux OS also
provide SGL (scatter gather list) APIs to support this usage.
THC uses PRD table (physical region descriptor) to support the corresponding OS kernel
SGL that describes the virtual to physical buffer mapping.
::
------------------------ -------------- --------------
| PRD table base address +----+ PRD table #1 +-----+ PRD Entry #1 |
------------------------ -------------- --------------
--------------
| PRD Entry #2 |
--------------
--------------
| PRD Entry #n |
--------------
The read DMA engine supports multiple PRD tables held within a circular buffer that allow the THC
to support multiple data buffers from the Touch IC. This allows host SW to arm the Read DMA engine
with multiple buffers, allowing the Touch IC to send multiple data frames to the THC without SW
interaction. This capability is required when the CPU processes touch frames slower than the
Touch IC can send them.
To simplify the design, SW assumes worst-case memory fragmentation. Therefore,each PRD table shall
contain the same number of PRD entries, allowing for a global register (per Touch IC) to hold the
number of PRD-entries per PRD table.
SW allocates up to 128 PRD tables per Read DMA engine as specified in the THC_M_PRT_RPRD_CNTRL.PCD
register field. The number of PRD tables should equal the number of data buffers.
Max OS memory fragmentation will be at a 4KB boundary, thus to address 1MB of virtually contiguous
memory 256 PRD entries are required for a single PRD Table. SW writes the number of PRD entries
for each PRD table in the THC_M_PRT_RPRD_CNTRL.PTEC register field. The PRD entry's length must be
multiple of 4KB except for the last entry in a PRD table.
SW allocates all the data buffers and PRD tables only once at host initialization.
3.4.2 PRD Write pointer and read pointer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As PRD tables are organized as a Circular Buffer (CB), a read pointer and a write pointer for a CB
are needed.
DMA HW consumes the PRD tables in the CB, one PRD entry at a time until the EOP bit is found set
in a PRD entry. At this point HW increments the PRD read pointer. Thus, the read pointer points
to the PRD which the DMA engine is currently processing. This pointer rolls over once the circular
buffer's depth has been traversed with bit[7] the Rollover bit. E.g. if the DMA CB depth is equal
to 4 entries (0011b), then the read pointers will follow this pattern (HW is required to honor
this behavior): 00h 01h 02h 03h 80h 81h 82h 83h 00h 01h ...
The write pointer is updated by SW. The write pointer points to location in the DMA CB, where the
next PRD table is going to be stored. SW needs to ensure that this pointer rolls over once the
circular buffer's depth has been traversed with Bit[7] as the rollover bit. E.g. if the DMA CB
depth is equal to 5 entries (0100b), then the write pointers will follow this pattern (SW is
required to honor this behavior): 00h 01h 02h 03h 04h 80h 81h 82h 83h 84h 00h 01h ..
3.4.3 PRD descriptor structure
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Intel THC uses PRD entry descriptor for every PRD entry. Every PRD entry descriptor occupies
128 bits memories:
=================== ======== ===============================================
struct field bit(s) description
=================== ======== ===============================================
dest_addr 53..0 destination memory address, as every entry
is 4KB, ignore lowest 10 bits of address.
reserved1 54..62 reserved
int_on_completion 63 completion interrupt enable bit, if this bit
set it means THC will trigger a completion
interrupt. This bit is set by SW driver.
len 87..64 how many bytes of data in this entry.
end_of_prd 88 end of PRD table bit, if this bit is set,
it means this entry is last entry in this PRD
table. This bit is set by SW driver.
hw_status 90..89 HW status bits
reserved2 127..91 reserved
=================== ======== ===============================================
And one PRD table can include up to 256 PRD entries, as every entries is 4K bytes, so every
PRD table can describe 1M bytes memory.
.. code-block:: c
struct thc_prd_table {
struct thc_prd_entry entries[PRD_ENTRIES_NUM];
};
In general, every PRD table means one HID touch data packet. Every DMA engine can support
up to 128 PRD tables (except write DMA, write DMA only has one PRD table). SW driver is responsible
to get max packet length from touch IC, and use this max packet length to create PRD entries for
each PRD table.
4. HIDSPI support (QuickSPI)
============================
Intel THC is total compatible with HIDSPI protocol, THC HW sequenser can accelerate HIDSPI
protocol transferring.
4.1 Reset Flow
--------------
- Call ACPI _RST method to reset Touch IC device.
- Read the reset response from TIC through PIO read.
- Issue a command to retrieve device descriptor from Touch IC through PIO write.
- Read the device descriptor from Touch IC through PIO read.
- If the device descriptor is valid, allocate DMA buffers and configure all DMA channels.
- Issue a command to retrieve report descriptor from Touch IC through DMA.
4.2 Input Report Data Flow
--------------------------
Basic Flow:
- Touch IC interrupts the THC Controller using an in-band THC interrupt.
- THC Sequencer reads the input report header by transmitting read approval as a signal
to the Touch IC to prepare for host to read from the device.
- THC Sequencer executes a Input Report Body Read operation corresponding to the value
reflected in “Input Report Length” field of the Input Report Header.
- THC DMA engine begins fetching data from the THC Sequencer and writes to host memory
at PRD entry 0 for the current CB PRD table entry. This process continues until the
THC Sequencer signals all data has been read or the THC DMA Read Engine reaches the
end of it's last PRD entry (or both).
- The THC Sequencer checks for the “Last Fragment Flag” bit in the Input Report Header.
If it is clear, the THC Sequencer enters an idle state.
- If the “Last Fragment Flag” bit is enabled the THC Sequencer enters End-of-Frame Processing.
THC Sequencer End of Frame Processing:
- THC DMA engine increments the read pointer of the Read PRD CB, sets EOF interrupt status
in RxDMA2 register (THC_M_PRT_READ_DMA_INT_STS_2).
- If THC EOF interrupt is enabled by the driver in the control register (THC_M_PRT_READ_DMA_CNTRL_2),
generates interrupt to software.
Sequence of steps to read data from RX DMA buffer:
- THC QuickSPI driver checks CB write Ptr and CB read Ptr to identify if any data frame in DMA
circular buffers.
- THC QuickSPI driver gets first unprocessed PRD table.
- THC QuickSPI driver scans all PRD entries in this PRD table to calculate the total frame size.
- THC QuickSPI driver copies all frame data out.
- THC QuickSPI driver checks the data type according to input report body, and calls related
callbacks to process the data.
- THC QuickSPI driver updates write Ptr.
4.3 Output Report Data Flow
---------------------------
Generic Output Report Flow:
- HID core calls raw_request callback with a request to THC QuickSPI driver.
- THC QuickSPI Driver converts request provided data into the output report packet and copies it
to THC's write DMA buffer.
- Start TxDMA to complete the write operation.
5. HIDI2C support (QuickI2C)
============================
5.1 Reset Flow
--------------
- Read device descriptor from Touch IC device through PIO write followed by read.
- If the device descriptor is valid, allocate DMA buffers and configure all DMA channels.
- Use PIO or TxDMA to write a SET_POWER request to TIC's command register, and check if the
write operation is successfully completed.
- Use PIO or TxDMA to write a RESET request to TIC's command register. If the write operation
is successfully completed, wait for reset response from TIC.
- Use SWDMA to read report descriptor through TIC's report descriptor register.
5.2 Input Report Data Flow
--------------------------
Basic Flow:
- Touch IC asserts the interrupt indicating that it has an interrupt to send to HOST.
THC Sequencer issues a READ request over the I2C bus. The HIDI2C device returns the
first 2 bytes from the HIDI2C device which contains the length of the received data.
- THC Sequencer continues the Read operation as per the size of data indicated in the
length field.
- THC DMA engine begins fetching data from the THC Sequencer and writes to host memory
at PRD entry 0 for the current CB PRD table entry. THC writes 2Bytes for length field
plus the remaining data to RxDMA buffer. This process continues until the THC Sequencer
signals all data has been read or the THC DMA Read Engine reaches the end of it's last
PRD entry (or both).
- THC Sequencer enters End-of-Input Report Processing.
- If the device has no more input reports to send to the host, it de-asserts the interrupt
line. For any additional input reports, device keeps the interrupt line asserted and
steps 1 through 4 in the flow are repeated.
THC Sequencer End of Input Report Processing:
- THC DMA engine increments the read pointer of the Read PRD CB, sets EOF interrupt status
in RxDMA 2 register (THC_M_PRT_READ_DMA_INT_STS_2).
- If THC EOF interrupt is enabled by the driver in the control register
(THC_M_PRT_READ_DMA_CNTRL_2), generates interrupt to software.
Sequence of steps to read data from RX DMA buffer:
- THC QuickI2C driver checks CB write Ptr and CB read Ptr to identify if any data frame in DMA
circular buffers.
- THC QuickI2C driver gets first unprocessed PRD table.
- THC QuickI2C driver scans all PRD entries in this PRD table to calculate the total frame size.
- THC QuickI2C driver copies all frame data out.
- THC QuickI2C driver call hid_input_report to send the input report content to HID core, which
includes Report ID + Report Data Content (remove the length field from the original report
data).
- THC QuickI2C driver updates write Ptr.
5.3 Output Report Data Flow
---------------------------
Generic Output Report Flow:
- HID core call THC QuickI2C raw_request callback.
- THC QuickI2C uses PIO or TXDMA to write a SET_REPORT request to TIC's command register. Report
type in SET_REPORT should be set to Output.
- THC QuickI2C programs TxDMA buffer with TX Data to be written to TIC's data register. The first
2 bytes should indicate the length of the report followed by the report contents including
Report ID.
6. THC Debugging
================
To debug THC, event tracing mechanism is used. To enable debug logs::
echo 1 > /sys/kernel/debug/tracing/events/intel_thc/enable
cat /sys/kernel/debug/tracing/trace
7. Reference
============
- HIDSPI: https://download.microsoft.com/download/c/a/0/ca07aef3-3e10-4022-b1e9-c98cea99465d/HidSpiProtocolSpec.pdf
- HIDI2C: https://download.microsoft.com/download/7/d/d/7dd44bb7-2a7a-4505-ac1c-7227d3d96d5b/hid-over-i2c-protocol-spec-v1-0.docx
linux-7.2.3/Documentation/hid/uhid.rst
+193
View File
@@ -0,0 +1,193 @@
======================================================
UHID - User-space I/O driver support for HID subsystem
======================================================
UHID allows user-space to implement HID transport drivers. Please see
hid-transport.rst for an introduction into HID transport drivers. This document
relies heavily on the definitions declared there.
With UHID, a user-space transport driver can create kernel hid-devices for each
device connected to the user-space controlled bus. The UHID API defines the I/O
events provided from the kernel to user-space and vice versa.
There is an example user-space application in ./samples/uhid/uhid-example.c
The UHID API
------------
UHID is accessed through a character misc-device. The minor number is allocated
dynamically so you need to rely on udev (or similar) to create the device node.
This is /dev/uhid by default.
If a new device is detected by your HID I/O Driver and you want to register this
device with the HID subsystem, then you need to open /dev/uhid once for each
device you want to register. All further communication is done by read()'ing or
write()'ing "struct uhid_event" objects. Non-blocking operations are supported
by setting O_NONBLOCK::
struct uhid_event {
__u32 type;
union {
struct uhid_create2_req create2;
struct uhid_output_req output;
struct uhid_input2_req input2;
...
} u;
};
The "type" field contains the ID of the event. Depending on the ID different
payloads are sent. You must not split a single event across multiple read()'s or
multiple write()'s. A single event must always be sent as a whole. Furthermore,
only a single event can be sent per read() or write(). Pending data is ignored.
If you want to handle multiple events in a single syscall, then use vectored
I/O with readv()/writev().
The "type" field defines the payload. For each type, there is a
payload-structure available in the union "u" (except for empty payloads). This
payload contains management and/or device data.
The first thing you should do is send a UHID_CREATE2 event. This will
register the device. UHID will respond with a UHID_START event. You can now
start sending data to and reading data from UHID. However, unless UHID sends the
UHID_OPEN event, the internally attached HID Device Driver has no user attached.
That is, you might put your device asleep unless you receive the UHID_OPEN
event. If you receive the UHID_OPEN event, you should start I/O. If the last
user closes the HID device, you will receive a UHID_CLOSE event. This may be
followed by a UHID_OPEN event again and so on. There is no need to perform
reference-counting in user-space. That is, you will never receive multiple
UHID_OPEN events without a UHID_CLOSE event. The HID subsystem performs
ref-counting for you.
You may decide to ignore UHID_OPEN/UHID_CLOSE, though. I/O is allowed even
though the device may have no users.
If you want to send data on the interrupt channel to the HID subsystem, you send
a HID_INPUT2 event with your raw data payload. If the kernel wants to send data
on the interrupt channel to the device, you will read a UHID_OUTPUT event.
Data requests on the control channel are currently limited to GET_REPORT and
SET_REPORT (no other data reports on the control channel are defined so far).
Those requests are always synchronous. That means, the kernel sends
UHID_GET_REPORT and UHID_SET_REPORT events and requires you to forward them to
the device on the control channel. Once the device responds, you must forward
the response via UHID_GET_REPORT_REPLY and UHID_SET_REPORT_REPLY to the kernel.
The kernel blocks internal driver-execution during such round-trips (times out
after a hard-coded period).
If your device disconnects, you should send a UHID_DESTROY event. This will
unregister the device. You can now send UHID_CREATE2 again to register a new
device.
If you close() the fd, the device is automatically unregistered and destroyed
internally.
write()
-------
write() allows you to modify the state of the device and feed input data into
the kernel. The kernel will parse the event immediately and if the event ID is
not supported, it will return -EOPNOTSUPP. If the payload is invalid, then
-EINVAL is returned, otherwise, the amount of data that was read is returned and
the request was handled successfully. O_NONBLOCK does not affect write() as
writes are always handled immediately in a non-blocking fashion. Future requests
might make use of O_NONBLOCK, though.
UHID_CREATE2:
This creates the internal HID device. No I/O is possible until you send this
event to the kernel. The payload is of type struct uhid_create2_req and
contains information about your device. You can start I/O now.
UHID_DESTROY:
This destroys the internal HID device. No further I/O will be accepted. There
may still be pending messages that you can receive with read() but no further
UHID_INPUT events can be sent to the kernel.
You can create a new device by sending UHID_CREATE2 again. There is no need to
reopen the character device.
UHID_INPUT2:
You must send UHID_CREATE2 before sending input to the kernel! This event
contains a data-payload. This is the raw data that you read from your device
on the interrupt channel. The kernel will parse the HID reports.
UHID_GET_REPORT_REPLY:
If you receive a UHID_GET_REPORT request you must answer with this request.
You must copy the "id" field from the request into the answer. Set the "err"
field to 0 if no error occurred or to EIO if an I/O error occurred.
If "err" is 0 then you should fill the buffer of the answer with the results
of the GET_REPORT request and set "size" correspondingly.
UHID_SET_REPORT_REPLY:
This is the SET_REPORT equivalent of UHID_GET_REPORT_REPLY. Unlike GET_REPORT,
SET_REPORT never returns a data buffer, therefore, it's sufficient to set the
"id" and "err" fields correctly.
read()
------
read() will return a queued output report. No reaction is required to any of
them but you should handle them according to your needs.
UHID_START:
This is sent when the HID device is started. Consider this as an answer to
UHID_CREATE2. This is always the first event that is sent. Note that this
event might not be available immediately after write(UHID_CREATE2) returns.
Device drivers might require delayed setups.
This event contains a payload of type uhid_start_req. The "dev_flags" field
describes special behaviors of a device. The following flags are defined:
- UHID_DEV_NUMBERED_FEATURE_REPORTS
- UHID_DEV_NUMBERED_OUTPUT_REPORTS
- UHID_DEV_NUMBERED_INPUT_REPORTS
Each of these flags defines whether a given report-type uses numbered
reports. If numbered reports are used for a type, all messages from
the kernel already have the report-number as prefix. Otherwise, no
prefix is added by the kernel.
For messages sent by user-space to the kernel, you must adjust the
prefixes according to these flags.
UHID_STOP:
This is sent when the HID device is stopped. Consider this as an answer to
UHID_DESTROY.
If you didn't destroy your device via UHID_DESTROY, but the kernel sends an
UHID_STOP event, this should usually be ignored. It means that the kernel
reloaded/changed the device driver loaded on your HID device (or some other
maintenance actions happened).
You can usually ignore any UHID_STOP events safely.
UHID_OPEN:
This is sent when the HID device is opened. That is, the data that the HID
device provides is read by some other process. You may ignore this event but
it is useful for power-management. As long as you haven't received this event
there is actually no other process that reads your data so there is no need to
send UHID_INPUT2 events to the kernel.
UHID_CLOSE:
This is sent when there are no more processes which read the HID data. It is
the counterpart of UHID_OPEN and you may as well ignore this event.
UHID_OUTPUT:
This is sent if the HID device driver wants to send raw data to the I/O
device on the interrupt channel. You should read the payload and forward it to
the device. The payload is of type "struct uhid_output_req".
This may be received even though you haven't received UHID_OPEN yet.
UHID_GET_REPORT:
This event is sent if the kernel driver wants to perform a GET_REPORT request
on the control channel as described in the HID specs. The report-type and
report-number are available in the payload.
The kernel serializes GET_REPORT requests so there will never be two in
parallel. However, if you fail to respond with a UHID_GET_REPORT_REPLY, the
request might silently time out.
Once you read a GET_REPORT request, you shall forward it to the HID device and
remember the "id" field in the payload. Once your HID device responds to the
GET_REPORT (or if it fails), you must send a UHID_GET_REPORT_REPLY to the
kernel with the exact same "id" as in the request. If the request already
timed out, the kernel will ignore the response silently. The "id" field is
never re-used, so conflicts cannot happen.
UHID_SET_REPORT:
This is the SET_REPORT equivalent of UHID_GET_REPORT. On receipt, you shall
send a SET_REPORT request to your HID device. Once it replies, you must tell
the kernel about it via UHID_SET_REPORT_REPLY.
The same restrictions as for UHID_GET_REPORT apply.
----------------------------------------------------
Written 2012, David Herrmann <dh.herrmann@gmail.com>