Resguardo inicial

linux-7.2.3/Documentation/driver-api/serial/driver.rst

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+====================
+Low Level Serial API
+====================
+
+
+This document is meant as a brief overview of some aspects of the new serial
+driver.  It is not complete, any questions you have should be directed to
+<rmk@arm.linux.org.uk>
+
+The reference implementation is contained within amba-pl011.c.
+
+
+
+Low Level Serial Hardware Driver
+--------------------------------
+
+The low level serial hardware driver is responsible for supplying port
+information (defined by uart_port) and a set of control methods (defined
+by uart_ops) to the core serial driver.  The low level driver is also
+responsible for handling interrupts for the port, and providing any
+console support.
+
+
+Console Support
+---------------
+
+The serial core provides a few helper functions.  This includes
+decoding command line arguments (uart_parse_options()).
+
+There is also a helper function (uart_console_write()) which performs a
+character by character write, translating newlines to CRLF sequences.
+Driver writers are recommended to use this function rather than implementing
+their own version.
+
+
+Locking
+-------
+
+It is the responsibility of the low level hardware driver to perform the
+necessary locking using port->lock.  There are some exceptions (which
+are described in the struct uart_ops listing below.)
+
+There are two locks.  A per-port spinlock, and an overall semaphore.
+
+From the core driver perspective, the port->lock locks the following
+data::
+
+	port->mctrl
+	port->icount
+	port->state->xmit.head (circ_buf->head)
+	port->state->xmit.tail (circ_buf->tail)
+
+The low level driver is free to use this lock to provide any additional
+locking.
+
+The port_sem semaphore is used to protect against ports being added/
+removed or reconfigured at inappropriate times. Since v2.6.27, this
+semaphore has been the 'mutex' member of the tty_port struct, and
+commonly referred to as the port mutex.
+
+
+uart_ops
+--------
+
+.. kernel-doc:: include/linux/serial_core.h
+   :identifiers: uart_ops
+
+Other functions
+---------------
+
+.. kernel-doc:: drivers/tty/serial/serial_core.c
+   :identifiers: uart_update_timeout uart_get_baud_rate uart_get_divisor
+           uart_match_port uart_write_wakeup uart_register_driver
+           uart_unregister_driver uart_suspend_port uart_resume_port
+           uart_add_one_port uart_remove_one_port uart_console_write
+           uart_parse_earlycon uart_parse_options uart_set_options
+           uart_get_lsr_info uart_handle_dcd_change uart_handle_cts_change
+           uart_try_toggle_sysrq
+
+.. kernel-doc:: include/linux/serial_core.h
+   :identifiers: uart_port_tx_limited uart_port_tx
+
+Other notes
+-----------
+
+It is intended some day to drop the 'unused' entries from uart_port, and
+allow low level drivers to register their own individual uart_port's with
+the core.  This will allow drivers to use uart_port as a pointer to a
+structure containing both the uart_port entry with their own extensions,
+thus::
+
+	struct my_port {
+		struct uart_port	port;
+		int			my_stuff;
+	};
+
+Modem control lines via GPIO
+----------------------------
+
+Some helpers are provided in order to set/get modem control lines via GPIO.
+
+.. kernel-doc:: drivers/tty/serial/serial_mctrl_gpio.c
+   :identifiers: mctrl_gpio_init mctrl_gpio_to_gpiod
+           mctrl_gpio_set mctrl_gpio_get mctrl_gpio_enable_ms
+           mctrl_gpio_disable_ms_sync mctrl_gpio_disable_ms_no_sync

linux-7.2.3/Documentation/driver-api/serial/index.rst

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+.. SPDX-License-Identifier: GPL-2.0
+
+==========================
+Support for Serial devices
+==========================
+
+.. toctree::
+    :maxdepth: 1
+
+
+    driver
+
+Serial drivers
+==============
+
+.. toctree::
+    :maxdepth: 1
+
+    serial-iso7816
+    serial-rs485

linux-7.2.3/Documentation/driver-api/serial/serial-iso7816.rst

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+=============================
+ISO7816 Serial Communications
+=============================
+
+1. Introduction
+===============
+
+  ISO/IEC7816 is a series of standards specifying integrated circuit cards (ICC)
+  also known as smart cards.
+
+2. Hardware-related considerations
+==================================
+
+  Some CPUs/UARTs (e.g., Microchip AT91) contain a built-in mode capable of
+  handling communication with a smart card.
+
+  For these microcontrollers, the Linux driver should be made capable of
+  working in both modes, and proper ioctls (see later) should be made
+  available at user-level to allow switching from one mode to the other, and
+  vice versa.
+
+3. Data Structures Already Available in the Kernel
+==================================================
+
+  The Linux kernel provides the serial_iso7816 structure (see [1]) to handle
+  ISO7816 communications. This data structure is used to set and configure
+  ISO7816 parameters in ioctls.
+
+  Any driver for devices capable of working both as RS232 and ISO7816 should
+  implement the iso7816_config callback in the uart_port structure. The
+  serial_core calls iso7816_config to do the device specific part in response
+  to TIOCGISO7816 and TIOCSISO7816 ioctls (see below). The iso7816_config
+  callback receives a pointer to struct serial_iso7816.
+
+4. Usage from user-level
+========================
+
+  From user-level, ISO7816 configuration can be get/set using the previous
+  ioctls. For instance, to set ISO7816 you can use the following code::
+
+	#include <linux/serial.h>
+
+	/* Include definition for ISO7816 ioctls: TIOCSISO7816 and TIOCGISO7816 */
+	#include <sys/ioctl.h>
+
+	/* Open your specific device (e.g., /dev/mydevice): */
+	int fd = open ("/dev/mydevice", O_RDWR);
+	if (fd < 0) {
+		/* Error handling. See errno. */
+	}
+
+	struct serial_iso7816 iso7816conf;
+
+	/* Reserved fields as to be zeroed */
+	memset(&iso7816conf, 0, sizeof(iso7816conf));
+
+	/* Enable ISO7816 mode: */
+	iso7816conf.flags |= SER_ISO7816_ENABLED;
+
+	/* Select the protocol: */
+	/* T=0 */
+	iso7816conf.flags |= SER_ISO7816_T(0);
+	/* or T=1 */
+	iso7816conf.flags |= SER_ISO7816_T(1);
+
+	/* Set the guard time: */
+	iso7816conf.tg = 2;
+
+	/* Set the clock frequency*/
+	iso7816conf.clk = 3571200;
+
+	/* Set transmission factors: */
+	iso7816conf.sc_fi = 372;
+	iso7816conf.sc_di = 1;
+
+	if (ioctl(fd_usart, TIOCSISO7816, &iso7816conf) < 0) {
+		/* Error handling. See errno. */
+	}
+
+	/* Use read() and write() syscalls here... */
+
+	/* Close the device when finished: */
+	if (close (fd) < 0) {
+		/* Error handling. See errno. */
+	}
+
+5. References
+=============
+
+ [1]    include/uapi/linux/serial.h

linux-7.2.3/Documentation/driver-api/serial/serial-rs485.rst

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+===========================
+RS485 Serial Communications
+===========================
+
+1. Introduction
+===============
+
+   EIA-485, also known as TIA/EIA-485 or RS-485, is a standard defining the
+   electrical characteristics of drivers and receivers for use in balanced
+   digital multipoint systems.
+   This standard is widely used for communications in industrial automation
+   because it can be used effectively over long distances and in electrically
+   noisy environments.
+
+2. Hardware-related Considerations
+==================================
+
+   Some CPUs/UARTs (e.g., Atmel AT91 or 16C950 UART) contain a built-in
+   half-duplex mode capable of automatically controlling line direction by
+   toggling RTS or DTR signals. That can be used to control external
+   half-duplex hardware like an RS485 transceiver or any RS232-connected
+   half-duplex devices like some modems.
+
+   For these microcontrollers, the Linux driver should be made capable of
+   working in both modes, and proper ioctls (see later) should be made
+   available at user-level to allow switching from one mode to the other, and
+   vice versa.
+
+3. Data Structures Already Available in the Kernel
+==================================================
+
+   The Linux kernel provides the struct serial_rs485 to handle RS485
+   communications. This data structure is used to set and configure RS485
+   parameters in the platform data and in ioctls.
+
+   The device tree can also provide RS485 boot time parameters
+   [#DT-bindings]_. The serial core fills the struct serial_rs485 from the
+   values given by the device tree when the driver calls
+   uart_get_rs485_mode().
+
+   Any driver for devices capable of working both as RS232 and RS485 should
+   implement the ``rs485_config`` callback and provide ``rs485_supported``
+   in the ``struct uart_port``. The serial core calls ``rs485_config`` to do
+   the device specific part in response to TIOCSRS485 ioctl (see below). The
+   ``rs485_config`` callback receives a pointer to a sanitizated struct
+   serial_rs485. The struct serial_rs485 userspace provides is sanitized
+   before calling ``rs485_config`` using ``rs485_supported`` that indicates
+   what RS485 features the driver supports for the ``struct uart_port``.
+   TIOCGRS485 ioctl can be used to read back the struct serial_rs485
+   matching to the current configuration.
+
+.. kernel-doc:: include/uapi/linux/serial.h
+   :identifiers: serial_rs485 uart_get_rs485_mode
+
+4. Usage from user-level
+========================
+
+   From user-level, RS485 configuration can be get/set using the previous
+   ioctls. For instance, to set RS485 you can use the following code::
+
+	#include <linux/serial.h>
+
+	/* Include definition for RS485 ioctls: TIOCGRS485 and TIOCSRS485 */
+	#include <sys/ioctl.h>
+
+	/* Open your specific device (e.g., /dev/mydevice): */
+	int fd = open ("/dev/mydevice", O_RDWR);
+	if (fd < 0) {
+		/* Error handling. See errno. */
+	}
+
+	struct serial_rs485 rs485conf;
+
+	/* Enable RS485 mode: */
+	rs485conf.flags |= SER_RS485_ENABLED;
+
+	/* Set logical level for RTS pin equal to 1 when sending: */
+	rs485conf.flags |= SER_RS485_RTS_ON_SEND;
+	/* or, set logical level for RTS pin equal to 0 when sending: */
+	rs485conf.flags &= ~(SER_RS485_RTS_ON_SEND);
+
+	/* Set logical level for RTS pin equal to 1 after sending: */
+	rs485conf.flags |= SER_RS485_RTS_AFTER_SEND;
+	/* or, set logical level for RTS pin equal to 0 after sending: */
+	rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND);
+
+	/* Set rts delay before send, if needed: */
+	rs485conf.delay_rts_before_send = ...;
+
+	/* Set rts delay after send, if needed: */
+	rs485conf.delay_rts_after_send = ...;
+
+	/* Set this flag if you want to receive data even while sending data */
+	rs485conf.flags |= SER_RS485_RX_DURING_TX;
+
+	if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) {
+		/* Error handling. See errno. */
+	}
+
+	/* Use read() and write() syscalls here... */
+
+	/* Close the device when finished: */
+	if (close (fd) < 0) {
+		/* Error handling. See errno. */
+	}
+
+5. Multipoint Addressing
+========================
+
+   The Linux kernel provides addressing mode for multipoint RS-485 serial
+   communications line. The addressing mode is enabled with
+   ``SER_RS485_ADDRB`` flag in struct serial_rs485. The struct serial_rs485
+   has two additional flags and fields for enabling receive and destination
+   addresses.
+
+   Address mode flags:
+	- ``SER_RS485_ADDRB``: Enabled addressing mode (sets also ADDRB in termios).
+	- ``SER_RS485_ADDR_RECV``: Receive (filter) address enabled.
+	- ``SER_RS485_ADDR_DEST``: Set destination address.
+
+   Address fields (enabled with corresponding ``SER_RS485_ADDR_*`` flag):
+	- ``addr_recv``: Receive address.
+	- ``addr_dest``: Destination address.
+
+   Once a receive address is set, the communication can occur only with the
+   particular device and other peers are filtered out. It is left up to the
+   receiver side to enforce the filtering. Receive address will be cleared
+   if ``SER_RS485_ADDR_RECV`` is not set.
+
+   Note: not all devices supporting RS485 support multipoint addressing.
+
+6. References
+=============
+
+.. [#DT-bindings]	Documentation/devicetree/bindings/serial/rs485.yaml