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

[Jonathan Cameron]

On Thu, 2 Jul 2026 19:58:32 +0100
Conor Dooley <conor@xxxxxxxxxx> wrote:

> On Wed, Jul 01, 2026 at 08:41:33PM +0100, Jonathan Cameron wrote:
> > On Fri, 26 Jun 2026 13:27:44 -0500
> > David Lechner <dlechner@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> > > >> ---
> > > >> 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?  
> 
> I think I would like a wording change from "allowed", to something that
> is akin to "If set, the hardware supports swapping...". Allows sounds
> too much like something that should be a userspace control.

I'd be inclined to talk a little more specifically.  What hardware?
It's the not the ADC that matters for this control, but rather whatever
is wired up to it. Otherwise agreed.  Maybe "If set, the connected
circuits are suitable for supporting ..." or something along those lines.

Thanks,

Jonathan