Re: [PATCH v3 2/8] dt-bindings: iio: adc: Add excitation current sources properties

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 10 Jul 2026 17:50:35 -0500
David Lechner <dlechner@baylibre.com> wrote:

> From: Kurt Borja <kuurtb@gmail.com>
> 
> Some ADCs incorporate current sources that provide excitation current to
> resistive temperature devices (RTDs), thermistors, diodes and other
> resistive sensors that require constant current biasing.
> 
> Signed-off-by: Kurt Borja <kuurtb@gmail.com>
> Acked-by: Conor Dooley <conor.dooley@microchip.com>
> Signed-off-by: David Lechner (TI) <dlechner@baylibre.com>
> ---
> v2 changes (compared to Kurt's RFC v2):
> * Make units nanoamps instead of microamps to fit known devices.
> * Drop bit about allowing single value for multiple channels.
> * Add bit about semantics of the array index.
> ---
>  Documentation/devicetree/bindings/iio/adc/adc.yaml | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/adc.yaml b/Documentation/devicetree/bindings/iio/adc/adc.yaml
> index 8f608bf0b24d..a21ed9ae4bab 100644
> --- a/Documentation/devicetree/bindings/iio/adc/adc.yaml
> +++ b/Documentation/devicetree/bindings/iio/adc/adc.yaml
> @@ -80,6 +80,26 @@ properties:
>        ADCs usually allow choosing between internal reference sources or a pair
>        of external pins.
>  
> +  excitation-channels:
> +    $ref: /schemas/types.yaml#/definitions/uint32-array
> +    description:
> +      Excitation current sources provide current to resistive temperature
> +      devices (RTDs), thermistors, diodes and other resistive sensors that
> +      require constant current biasing.
> +
> +      This array describes the mux configuration of the excitation current
> +      sources.

I wonder if we should have something here to reference what 'channels' means
and that it may reference the same numbers as reg / single-channel / diff-channels.

Bit tricky as I guess maybe it won't always do that. There are devices that use
separate sets of pins for this but still have several sets of those.

Maybe vague is our friend!


> +
> +  excitation-current-nanoamp:
> +    description:
> +      Excitation current sources provide current to resistive temperature
> +      devices (RTDs), thermistors, diodes and other resistive sensors that
> +      require constant current biasing.
> +
> +      This array describes the current configuration of the excitation current
> +      sources. The index in the array corresponds to the same index in the
> +      excitation-channels array.
> +
>  anyOf:
>    - oneOf:
>        - required:
>