Re: [PATCH v2 2/8] dt-bindings: iio: adc: Add excitation current sources properties

[David Lechner <dlechner@baylibre.com>]

On 7/1/26 2:39 PM, Jonathan Cameron wrote:
> On Thu, 25 Jun 2026 16:55:04 -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>
>> 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 12800737d4fb..860601ec5334 100644
>> --- a/Documentation/devicetree/bindings/iio/adc/adc.yaml
>> +++ b/Documentation/devicetree/bindings/iio/adc/adc.yaml
>> @@ -81,6 +81,26 @@ properties:
>>        ADCs usually allow choosing between internal reference sources or a pair
>>        of external pins.
>>  
>> +  excitation-channels:
> 
> How would this apply if a device provided excitation on pins that didn't correspond
> to channels? i.e. some extra ones.  Perhaps such a device that also supports
> configuration (rather than a static set up) would just need a different binding.
> Feels like I'm creating a corner case we may never see :)
> 
We could have e.g. a ti,current-output flag to say that this
is just a current output channel if we really needed this.
In that case, I think we would use single-channel to specify
the pin and not have excitation-channels or excitation-current-nanoamp.
But as you guessed, this not something we would expect anyone
to actually do with these chips, so we'll leave that out.