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linux-7.2.3/Documentation/devicetree/bindings/iio/afe/current-sense-amplifier.yaml

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+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/afe/current-sense-amplifier.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Current Sense Amplifier
+
+maintainers:
+  - Peter Rosin <peda@axentia.se>
+
+description: |
+  When an io-channel measures the output voltage from a current sense
+  amplifier, the interesting measurement is almost always the current
+  through the sense resistor, not the voltage output. This binding
+  describes such a current sense circuit.
+
+properties:
+  compatible:
+    const: current-sense-amplifier
+
+  io-channels:
+    maxItems: 1
+    description: |
+      Channel node of a voltage io-channel.
+
+  "#io-channel-cells":
+    const: 0
+
+  sense-resistor-micro-ohms:
+    description: The sense resistance.
+
+  sense-gain-mult:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Amplifier gain multiplier. The default is <1>.
+
+  sense-gain-div:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: Amplifier gain divider. The default is <1>.
+
+required:
+  - compatible
+  - io-channels
+  - sense-resistor-micro-ohms
+
+additionalProperties: false
+
+examples:
+  - |
+    sysi {
+        compatible = "current-sense-amplifier";
+        #io-channel-cells = <0>;
+        io-channels = <&tiadc 0>;
+
+        sense-resistor-micro-ohms = <20000>;
+        sense-gain-mult = <50>;
+    };
+...

linux-7.2.3/Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml

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+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/afe/current-sense-shunt.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Current Sense Shunt
+
+maintainers:
+  - Peter Rosin <peda@axentia.se>
+
+description: |
+  When an io-channel measures the voltage over a current sense shunt,
+  the interesting measurement is almost always the current through the
+  shunt, not the voltage over it. This binding describes such a current
+  sense circuit.
+
+properties:
+  compatible:
+    const: current-sense-shunt
+
+  io-channels:
+    maxItems: 1
+    description: |
+      Channel node of a voltage io-channel.
+
+  "#io-channel-cells":
+    const: 0
+
+  shunt-resistor-micro-ohms:
+    description: The shunt resistance.
+
+required:
+  - compatible
+  - io-channels
+  - shunt-resistor-micro-ohms
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        tiadc: adc@48 {
+            compatible = "ti,ads1015";
+            reg = <0x48>;
+            #io-channel-cells = <1>;
+
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            channel@0 { /* IN0,IN1 differential */
+                reg = <0>;
+                ti,gain = <1>;
+                ti,datarate = <4>;
+            };
+        };
+    };
+    sysi {
+        compatible = "current-sense-shunt";
+        io-channels = <&tiadc 0>;
+        #io-channel-cells = <0>;
+
+        /* Divide the voltage by 3300000/1000000 (or 3.3) for the current. */
+        shunt-resistor-micro-ohms = <3300000>;
+    };
+...

linux-7.2.3/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml

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+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/afe/temperature-sense-rtd.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Temperature Sense RTD
+
+maintainers:
+  - Liam Beguin <liambeguin@gmail.com>
+
+description: |
+  RTDs (Resistance Temperature Detectors) are a kind of temperature sensors
+  used to get a linear voltage to temperature reading within a give range
+  (usually 0 to 100 degrees Celsius).
+
+  When an io-channel measures the output voltage across an RTD such as a
+  PT1000, the interesting measurement is almost always the corresponding
+  temperature, not the voltage output. This binding describes such a circuit.
+
+  The general transfer function here is (using SI units)
+
+    V = R(T) * iexc
+    R(T) = r0 * (1 + alpha * T)
+    T = 1 / (alpha * r0 * iexc) * (V - r0 * iexc)
+
+  The following circuit matches what's in the examples section.
+
+           5V0
+          -----
+            |
+        +---+----+
+        |  R 5k  |
+        +---+----+
+            |
+            V 1mA
+            |
+            +---- Vout
+            |
+        +---+----+
+        | PT1000 |
+        +---+----+
+            |
+          -----
+           GND
+
+properties:
+  compatible:
+    const: temperature-sense-rtd
+
+  io-channels:
+    maxItems: 1
+    description: |
+      Channel node of a voltage io-channel.
+
+  '#io-channel-cells':
+    const: 0
+
+  excitation-current-microamp:
+    description: The current fed through the RTD sensor.
+
+  alpha-ppm-per-celsius:
+    description: |
+      alpha can also be expressed in micro-ohms per ohm Celsius. It's a linear
+      approximation of the resistance versus temperature relationship
+      between 0 and 100 degrees Celsius.
+
+      alpha = (R_100 - R_0) / (100 * R_0)
+
+      Where, R_100 is the resistance of the sensor at 100 degrees Celsius, and
+      R_0 (or r-naught-ohms) is the resistance of the sensor at 0 degrees
+      Celsius.
+
+      Pure platinum has an alpha of 3925. Industry standards such as IEC60751
+      and ASTM E-1137 specify an alpha of 3850.
+
+  r-naught-ohms:
+    description: |
+      Resistance of the sensor at 0 degrees Celsius.
+      Common values are 100 for PT100, 500 for PT500, and 1000 for PT1000
+
+additionalProperties: false
+required:
+  - compatible
+  - io-channels
+  - excitation-current-microamp
+  - alpha-ppm-per-celsius
+  - r-naught-ohms
+
+examples:
+  - |
+    pt1000_1: temperature-sensor0 {
+        compatible = "temperature-sense-rtd";
+        #io-channel-cells = <0>;
+        io-channels = <&temp_adc1 0>;
+
+        excitation-current-microamp = <1000>; /* i = U/R = 5 / 5000 */
+        alpha-ppm-per-celsius = <3908>;
+        r-naught-ohms = <1000>;
+    };
+...

linux-7.2.3/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml

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+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/afe/temperature-transducer.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Temperature Transducer
+
+maintainers:
+  - Liam Beguin <liambeguin@gmail.com>
+
+description: |
+  A temperature transducer is a device that converts a thermal quantity
+  into any other physical quantity. This binding applies to temperature to
+  voltage (like the LTC2997), and temperature to current (like the AD590)
+  linear transducers.
+  In both cases these are assumed to be connected to a voltage ADC.
+
+  When an io-channel measures the output voltage of a temperature analog front
+  end such as a temperature transducer, the interesting measurement is almost
+  always the corresponding temperature, not the voltage output. This binding
+  describes such a circuit.
+
+  The general transfer function here is (using SI units)
+    V(T) = Rsense * Isense(T)
+    T = (Isense(T) / alpha) + offset
+    T = 1 / (Rsense * alpha) * (V + offset * Rsense * alpha)
+
+  When using a temperature to voltage transducer, Rsense is set to 1.
+
+  The following circuits show a temperature to current and a temperature to
+  voltage transducer that can be used with this binding.
+
+           VCC
+          -----
+            |
+        +---+---+
+        | AD590 |                               VCC
+        +---+---+                              -----
+            |                                    |
+            V proportional to T             +----+----+
+            |                          D+ --+         |
+            +---- Vout                      | LTC2997 +--- Vout
+            |                          D- --+         |
+        +---+----+                          +---------+
+        | Rsense |                               |
+        +---+----+                             -----
+            |                                   GND
+          -----
+           GND
+
+properties:
+  compatible:
+    const: temperature-transducer
+
+  io-channels:
+    maxItems: 1
+    description: |
+      Channel node of a voltage io-channel.
+
+  '#io-channel-cells':
+    const: 0
+
+  sense-offset-millicelsius:
+    description: |
+      Temperature offset.
+      This offset is commonly used to convert from Kelvins to degrees Celsius.
+      In that case, sense-offset-millicelsius would be set to <(-273150)>.
+    default: 0
+
+  sense-resistor-ohms:
+    description: |
+      The sense resistor.
+      By default sense-resistor-ohms cancels out the resistor making the
+      circuit behave like a temperature transducer.
+    default: 1
+
+  alpha-ppm-per-celsius:
+    description: |
+      Sometimes referred to as output gain, slope, or temperature coefficient.
+
+      alpha is expressed in parts per million which can be micro-amps per
+      degrees Celsius or micro-volts per degrees Celsius. The is the main
+      characteristic of a temperature transducer and should be stated in the
+      datasheet.
+
+additionalProperties: false
+
+required:
+  - compatible
+  - io-channels
+  - alpha-ppm-per-celsius
+
+examples:
+  - |
+    ad950: temperature-sensor-0 {
+        compatible = "temperature-transducer";
+        #io-channel-cells = <0>;
+        io-channels = <&temp_adc 3>;
+
+        sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */
+        sense-resistor-ohms = <8060>;
+        alpha-ppm-per-celsius = <1>; /* 1 uA/K */
+    };
+  - |
+    znq_tmp: temperature-sensor-1 {
+        compatible = "temperature-transducer";
+        #io-channel-cells = <0>;
+        io-channels = <&temp_adc 2>;
+
+        sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */
+        alpha-ppm-per-celsius = <4000>; /* 4 mV/K */
+    };
+...

linux-7.2.3/Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml

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+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/afe/voltage-divider.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Voltage divider
+
+maintainers:
+  - Peter Rosin <peda@axentia.se>
+
+description: |
+  When an io-channel measures the midpoint of a voltage divider, the
+  interesting voltage is often the voltage over the full resistance
+  of the divider. This binding describes the voltage divider in such
+  a circuit.
+
+    Vin ----.
+            |
+         .-----.
+         |  R  |
+         '-----'
+            |
+            +---- Vout
+            |
+         .-----.
+         | Rout|
+         '-----'
+            |
+           GND
+
+properties:
+  compatible:
+    const: voltage-divider
+
+  io-channels:
+    maxItems: 1
+    description: |
+      Channel node of a voltage io-channel.
+
+  '#io-channel-cells':
+    description:
+      In addition to consuming the measurement services of a voltage
+      output channel, the voltage divider can act as a provider of
+      measurement services to other devices. This is particularly
+      useful in scenarios wherein an ADC has an analog frontend,
+      such as a voltage divider, and then consuming its raw value
+      isn't interesting. In this case, the voltage before the divider
+      is desired.
+    const: 1
+
+  output-ohms:
+    description:
+      Resistance Rout over which the output voltage is measured. See full-ohms.
+
+  full-ohms:
+    description:
+      Resistance R + Rout for the full divider. The io-channel is scaled by
+      the Rout / (R + Rout) quotient.
+
+required:
+  - compatible
+  - io-channels
+  - output-ohms
+  - full-ohms
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    /*
+     * The system voltage is circa 12V, but divided down with a 22/222
+     * voltage divider (R = 200 Ohms, Rout = 22 Ohms) and fed to an ADC.
+     */
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        maxadc: adc@0 {
+            compatible = "maxim,max1027";
+            reg = <0>;
+            #io-channel-cells = <1>;
+            interrupt-parent = <&gpio5>;
+            interrupts = <15 IRQ_TYPE_EDGE_RISING>;
+            spi-max-frequency = <1000000>;
+        };
+    };
+    sysv {
+        compatible = "voltage-divider";
+        io-channels = <&maxadc 1>;
+
+        /* Scale the system voltage by 22/222 to fit the ADC range. */
+        output-ohms = <22>;
+        full-ohms = <222>; /* 200 + 22 */
+    };
+...