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

Rob Herring
2021-06-04T21:17:07Z

On Sat, May 29, 2021 at 08:59:15PM -0400, Liam Beguin wrote:
> From: Liam Beguin <lvb@xiphos.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@xiphos.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@xiphos.com>
> +
> +description: |
> + When an io-channel measures the output voltage across an RTD such as a

What's an RTD? Not defined anywhere here.

> + 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

Doesn't this belong in the provider?

> +
> + 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.

Is there a max and min value?

> +
> + r-naught-ohms:
> + description: |
> + Resistance of the sensor at 0 degrees Celsius.
> + Common values are 100 for PT100 and 1000 for PT1000.

max or min?

> +
> +additionalProperties: false

blank line here.

> +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@vger.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