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Subject: Re: [PATCH] dt-bindings: iio: afe: current-sense-shunt: add
 io-channel-cells
To:     Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Rob Herring <robh+dt@kernel.org>, linux-iio@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210506150637.35288-1-krzysztof.kozlowski@canonical.com>
From:   Peter Rosin <peda@axentia.se>
Organization: Axentia Technologies AB
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Date:   Sat, 8 May 2021 00:44:58 +0200
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Hi!

On 2021-05-06 17:06, Krzysztof Kozlowski wrote:
> The current-sense-shunt is an IIO provider thus can be referenced by IIO
> consumers (via "io-channels" property in consumer device node).
> Such provider is required to describe number of cells used in phandle
> lookup with "io-channel-cells" property.  This also fixes dtbs_check
> warnings like:
> 
>   arch/arm/boot/dts/s5pv210-fascinate4g.dt.yaml: current-sense-shunt:
>     '#io-channel-cells' does not match any of the regexes: 'pinctrl-[0-9]+'
> 
> Fixes: ce66e52b6c16 ("dt-bindings:iio:afe:current-sense-shunt: txt to yaml conversion.")
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
> ---
>  .../devicetree/bindings/iio/afe/current-sense-shunt.yaml     | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml b/Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml
> index 90439a8dc785..05166d8a3124 100644
> --- a/Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml
> +++ b/Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml
> @@ -24,12 +24,16 @@ properties:
>      description: |
>        Channel node of a voltage io-channel.
>  
> +  "#io-channel-cells":
> +    const: 0
> +
>    shunt-resistor-micro-ohms:
>      description: The shunt resistance.
>  
>  required:
>    - compatible
>    - io-channels
> +  - "#io-channel-cells"
>    - shunt-resistor-micro-ohms

I know I'm listed as maintainer and all, but I have not kept up with the yaml
conversion. Sorry. So, given that I might very well fundamentally misunderstand
something, it does not sound correct that #io-channel-cells is now "required".
I regard it as optional, and only needed if some other in-kernel driver is
consuming the sensed current. What am I missing?

Also, whatever is done in this binding should preferably also be done in the
two "sister" afe bindings, i.e. current-sense-amplifier and voltage-divider.

Cheers,
Peter

>  additionalProperties: false
> @@ -57,6 +61,7 @@ examples:
>      sysi {
>          compatible = "current-sense-shunt";
>          io-channels = <&tiadc 0>;
> +        #io-channel-cells = <0>;
>  
>          /* Divide the voltage by 3300000/1000000 (or 3.3) for the current. */
>          shunt-resistor-micro-ohms = <3300000>;
>