Re: [PATCH v2 4/8] dt-bindings: iio: adc: add input-channel-rotation property

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 26 Jun 2026 13:27:44 -0500
David Lechner <dlechner@baylibre.com> wrote:

> On 6/26/26 11:14 AM, Conor Dooley wrote:
> > On Thu, Jun 25, 2026 at 04:55:06PM -0500, David Lechner (TI) wrote:  
> >> Add a generic input-channel-rotation property to adc.yaml. This is a
> >> feature seen frequently in ADCs that are designed to measure resistive
> >> loads, such as RTDs and strain gauges. Enabling this can reduce offset
> >> errors by swapping the positive and negative input channels on every
> >> other conversion. This can have side-effects in timing and filter
> >> response, so it is not always desirable to enable this feature in some
> >> applications. Therefore, it is best to make this a property that can be
> >> enabled or disabled in the device tree.
> >>
> >> Signed-off-by: David Lechner (TI) <dlechner@baylibre.com>
> >> ---
> >> v2 changes:
> >> * New patch.
> >> ---
> >>  Documentation/devicetree/bindings/iio/adc/adc.yaml | 7 +++++++
> >>  1 file changed, 7 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/iio/adc/adc.yaml b/Documentation/devicetree/bindings/iio/adc/adc.yaml
> >> index 9ec1f447b565..3d52c00922c9 100644
> >> --- a/Documentation/devicetree/bindings/iio/adc/adc.yaml
> >> +++ b/Documentation/devicetree/bindings/iio/adc/adc.yaml
> >> @@ -81,6 +81,13 @@ properties:
> >>        ADCs usually allow choosing between internal reference sources or a pair
> >>        of external pins.
> >>  
> >> +  input-channel-rotation:  
> 
> I got some internal feedback after I sent this patch that "chopping" is the
> more common terminology for this feature industry-wide, so in the next revision
> I plan to change it into `input-chopping`.
> 
> >> +    type: boolean
> >> +    description:
> >> +      If set, the positive and negative input channels are allowed to be swapped
> >> +      on every other conversion to reduce offset errors. This is also referred
> >> +      to as "chop" in some datasheets.  
> > 
> > "allowed to be swapped" means that this property says the feature can be
> > used, but userspace may have to be the thing that ultimately turns it
> > on?  
> 
> No, I don't expect a userspace control for it. More like the driver should
> enable it when possible, but a driver doesn't necessarily have to implement
> it and everything will still work, just with less accuracy.

Perhaps we need something in this text to say when it should not be set
in dt?

Jonathan

> 
> >   
> >> +
> >>    excitation-channels:
> >>      $ref: /schemas/types.yaml#/definitions/uint32-array
> >>      description:
> >>
> >> -- 
> >> 2.43.0
> >>  
>