Re: [PATCH v3 4/8] dt-bindings: iio: adc: add input-chopping property

[Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>]

On Mon, 13 Jul 2026 09:55:53 -0500
David Lechner <dlechner@baylibre.com> wrote:

> On 7/12/26 8:34 PM, Jonathan Cameron wrote:
> > On Fri, 10 Jul 2026 17:50:37 -0500
> > "David Lechner (TI)" <dlechner@baylibre.com> wrote:
> >   
> >> Add a generic input-chopping 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>
> >> ---
> >> v3 changes:
> >> * Renamed property to input-chopping to reflect more common terminology.
> >> * Removed "allowed" from the description.
> >> * Extended description to explain when it should not be used.
> >>
> >> v2 changes:
> >> * New patch.
> >> ---
> >>  Documentation/devicetree/bindings/iio/adc/adc.yaml | 8 ++++++++
> >>  1 file changed, 8 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/iio/adc/adc.yaml b/Documentation/devicetree/bindings/iio/adc/adc.yaml
> >> index 308857f11220..c408feebd46d 100644
> >> --- a/Documentation/devicetree/bindings/iio/adc/adc.yaml
> >> +++ b/Documentation/devicetree/bindings/iio/adc/adc.yaml
> >> @@ -80,6 +80,14 @@ properties:
> >>        ADCs usually allow choosing between internal reference sources or a pair
> >>        of external pins.
> >>  
> >> +  input-chopping:
> >> +    type: boolean
> >> +    description:
> >> +      If set, the positive and negative input channels are swapped on every
> >> +      other conversion to reduce offset error. This generally comes at the
> >> +      expense of added settling time between conversions, so should be omitted
> >> +      on systems with high-frequency signals or high data rate requirements.  
> > 
> > I'm lazy so I didn't check back, but in my mental model of this, the DT is simply
> > saying that the analog circuitry is suitable for doing chopping.  Driver decision
> > on whether to do it.  Perhaps we can reword it for that?  
> 
> Heh, that was the "allowed" part that I removed.
> 
> I think this is really more of a design decision between the tradeoff
> of less noise vs. data rate. By setting this property, we are saying
> we should favor less noise. So I think it is more about the expected
> signal than the circuitry.
> 
> So not sure that I would add anything here.
Fair enough.  Given the driver can always ignore what is in DT I guess it
is fine as is.

Thanks,

Jonathan

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