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Subject[PATCH v3 10/10] dt-bindings: iio: afe: add bindings for temperature transducers
Date
From: Liam Beguin <lvb@xiphos.com>

An ADC is often used to measure other quantities indirectly.
This binding describe one case, the measurement of a temperature
through a temperature transducer (either voltage or current).

Signed-off-by: Liam Beguin <lvb@xiphos.com>
---
.../iio/afe/temperature-transducer.yaml | 111 ++++++++++++++++++
MAINTAINERS | 1 +
2 files changed, 112 insertions(+)
create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml

diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml
new file mode 100644
index 000000000000..d16c0ade2271
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml
@@ -0,0 +1,111 @@
+# 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 <lvb@xiphos.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: 1
+
+ sense-offset-millicelsius:
+ description: |
+ Temperature offset. The default is <0>.
+ This offset is commonly used to convert from Kelvins to degrees Celsius.
+ In that case, sense-offset-millicelsius would be set to <(-273150)>.
+
+ sense-resistor-ohms:
+ description: |
+ The sense resistor. Defaults to <1>.
+ Set sense-resistor-ohms to <1> when using a temperature to voltage
+ transducer.
+
+ 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 = <1>;
+ 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 = <1>;
+ io-channels = <&temp_adc 2>;
+
+ sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */
+ alpha-ppm-per-celsius = <4000>; /* 4 mV/K */
+ };
+...
diff --git a/MAINTAINERS b/MAINTAINERS
index ed80e671a16a..e9e11c3ea4e3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8903,6 +8903,7 @@ R: Peter Rosin <peda@axentia.se>
L: linux-iio@vger.kernel.org
S: Maintained
F: Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
+F: Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml

IKANOS/ADI EAGLE ADSL USB DRIVER
M: Matthieu Castet <castet.matthieu@free.fr>
--
2.30.1.489.g328c10930387
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