linux-kernel - [PATCH v1 7/9] dt-bindings: iio: afe: add binding for temperature-sense-rtd

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Date:   Sat, 29 May 2021 20:59:15 -0400
From:   Liam Beguin <liambeguin@...il.com>
To:     liambeguin@...il.com, peda@...ntia.se, jic23@...nel.org,
        lars@...afoo.de, pmeerw@...erw.net
Cc:     linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org, robh+dt@...nel.org
Subject: [PATCH v1 7/9] dt-bindings: iio: afe: add binding for temperature-sense-rtd

From: Liam Beguin <lvb@...hos.com>

An ADC is often used to measure other quantities indirectly. This
binding describe one cases, the measurement of a temperature through
the voltage across an RTD resistor such as a PT1000.

Signed-off-by: Liam Beguin <lvb@...hos.com>
---
 .../iio/afe/temperature-sense-rtd.yaml        | 65 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 2 files changed, 66 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml

diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
new file mode 100644
index 000000000000..4798eda6e533
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
@@ -0,0 +1,65 @@
+# 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 <lvb@...hos.com>
+
+description: |
+  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.
+
+properties:
+  compatible:
+    const: temperature-sense-rtd
+
+  io-channels:
+    maxItems: 1
+    description: |
+      Channel node of a voltage io-channel.
+
+  '#io-channel-cells':
+    const: 1
+
+  excitation-current-microamp:
+    description: The current fed through the RTD sensor.
+
+  alpha-micro-ohms-per-ohm-celsius:
+    description: |
+      Linear approximation of the resistance versus temperature relationship
+      between 0 and 100 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 and 1000 for PT1000.
+
+additionalProperties: false
+required:
+  - compatible
+  - io-channels
+  - excitation-current-microamp
+  - alpha-micro-ohms-per-ohm-celsius
+  - r-naught-ohms
+
+examples:
+  - |
+    pt1000_1: iio-rescale0 {
+        compatible = "temperature-sense-rtd";
+        #io-channel-cells = <1>;
+        io-channels = <&temp_adc1 0>;
+
+        excitation-current-microamp = <1000>;
+        alpha-micro-ohms-per-ohm-celsius = <3908>;
+        r-naught-ohms = <1000>;
+    };
+
+...
diff --git a/MAINTAINERS b/MAINTAINERS
index d3ab0ccc34ab..a7279af85adb 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8721,6 +8721,7 @@ L:	linux-iio@...r.kernel.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/iio/afe/current-sense-amplifier.yaml
 F:	Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml
+F:	Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
 F:	Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml
 F:	drivers/iio/afe/iio-rescale.c
 
-- 
2.30.1.489.g328c10930387