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

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Date:   Tue, 1 Jun 2021 17:47:13 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Liam Beguin <liambeguin@...il.com>
CC:     <peda@...ntia.se>, <jic23@...nel.org>, <lars@...afoo.de>,
        <pmeerw@...erw.net>, <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

On Sat, 29 May 2021 20:59:16 -0400
Liam Beguin <liambeguin@...il.com> 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

What about such a sensor connected to a current ADC? That was what I was
immediately expecting when I saw the naming.

You could daisy chain this with the current-sense-resistor AFE though
that does seem overly messy.

Anyhow this should be called something that reflects the presence of
that sense resitor.

> +
> +  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.
> +
> +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