linux-kernel - Re: [PATCH v1 8/9] dt-bindings: iio: afe: add binding for temperature-sense-current

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Message-ID: <9f38ad0a-0a08-458d-b721-f4d424cecc6d@axentia.se>
Date:   Mon, 31 May 2021 09:28:26 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Liam Beguin <liambeguin@...il.com>, 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: Re: [PATCH v1 8/9] dt-bindings: iio: afe: add binding for
 temperature-sense-current

Hi!

On 2021-05-30 02:59, Liam Beguin wrote:
> 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
> a current sense amplifier (such as an AD590) and a sense resistor.
> 
> Signed-off-by: Liam Beguin <lvb@...hos.com>
> ---
>  .../iio/afe/temperature-sense-current.yaml    | 61 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  2 files changed, 62 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-sense-current.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-sense-current.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-sense-current.yaml
> new file mode 100644
> index 000000000000..1bac74486102
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/afe/temperature-sense-current.yaml
> @@ -0,0 +1,61 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/afe/temperature-sense-current.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Temperature Sense Current
> +
> +maintainers:
> +  - Liam Beguin <lvb@...hos.com>
> +
> +description: |
> +  When an io-channel measures the output voltage for a temperature current
> +  sense amplifier such as the AD950, the interesting measurement is almost
> +  always the corresponding temperature, not the voltage output.
> +  This binding describes such a circuit.
> +
> +properties:
> +  compatible:
> +    const: temperature-sense-current
> +
> +  io-channels:
> +    maxItems: 1
> +    description: |
> +      Channel node of a voltage io-channel.
> +
> +  '#io-channel-cells':
> +    const: 1
> +
> +  sense-resistor-ohms:
> +    description: The sense resistance.
> +
> +  alpha-micro-amps-per-degree:
> +    description: |
> +      Linear output current gain of the temperature IC.
> +
> +  use-kelvin-scale:
> +    type: boolean
> +    description: |
> +      Boolean indicating if alpha uses Kelvin degrees instead of Celsius.

It's "kelvin", not "Kelvin degrees", and it's "degrees Celsius".

But what exactly is this property for? We always want degrees Celsius, don't we,
and any offset can be handled...with an offset. No?

Cheers,
Peter

> +
> +additionalProperties: false
> +required:
> +  - compatible
> +  - io-channels
> +  - sense-resistor-ohms
> +  - alpha-micro-amps-per-degree
> +
> +examples:
> +  - |
> +    ad590: iio-rescale0 {
> +        compatible = "temperature-sense-current";
> +        #io-channel-cells = <1>;
> +        io-channels = <&temp_adc 2>;
> +
> +        sense-resistor-ohms = <8060>;
> +        use-kelvin-scale;
> +        alpha-micro-amps-per-degree = <1>;
> +    };
> +
> +...
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a7279af85adb..0eb7fcd94b66 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-current.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
> 

-- 
Peter Rosin
+46 730 746 224
Axentia Technologies AB