Re: [PATCH v8 v8 02/11] dt-bindings: iio: adc: hx711: add VSUP supply property

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 19 May 2026 02:47:44 +0530
Piyush Patle <piyushpatle228@gmail.com> wrote:

> On Tue, May 12, 2026 at 5:38 PM Jonathan Cameron <jic23@kernel.org> wrote:
> >
> > On Tue, 12 May 2026 13:06:22 +0100
> > Jonathan Cameron <jic23@kernel.org> wrote:
> >  
> > > On Mon, 11 May 2026 23:13:27 +0530
> > > Piyush Patle <piyushpatle228@gmail.com> wrote:
> > >  
> > > > Document the optional VSUP supply used by the HX711 on-chip regulator.
> > > >
> > > > Signed-off-by: Piyush Patle <piyushpatle228@gmail.com>
> > > > Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> > > > Acked-by: Conor Dooley <conor.dooley@microchip.com>
> > > > ---  
> > >
> > > I got curious given the driver doesn't yet turn this on and wanted
> > > to just sanity check it via a datasheet.
> > >
> > > Why are we including this one but not dvdd-supply?  The suggested
> > > wiring does connect them to the same supply but it's external to the
> > > chip so in theory they might not be.  Curiously dvdd supply is allowed
> > > to be 0.1 V lower than vsup-supply.  
> The HX711 does have a DVDD pin, but it is the output of the internal
> LDO and is normally just bypassed to ground. VSUP is the rail supplied by
> the board, so that was the one I documented here.

Not according to the diagram in figure 1 of
https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/hx711_english.pdf

That clearly shows DVDD connected to same input supply as VSUP.
There is a note in there to say that if the internal regulator is not
used VSUP should always be connected to the higher of DVDD and AVDD.


> That said, dvdd-supply is already allowed for HX711 nodes by patch 04,
> as only vref-supply is forbidden for HX711. So the binding does not block
> a board from describing DVDD if needed.

Agreed you add it later, but it should be in this patch that is adding missing
dt-bindings for the existing part.

> The driver does not use DVDD for HX711 today, but explicit support can be
> added later if there is a real user for it.

We should make dt-bindings complete.  That doesn't mean the driver has to
use them though!

Hence I'd like to see dvdd added in this patch rather than later with
a statement of why it is used for the hx711.  As far as I can tell it should
really be required and documented as a bug in the original binding.

Jonathan


> >
> > I should have said, given there is nothing wrong with what you have here
> > and the above is a possible additional change - applied to the testing
> > branch of iio.git.
> >
> > Thanks,
> >
> > Jonathan
> >  
> Thanks for applying patches 01-03.
> > >  
> > > >  Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml | 4 ++++
> > > >  1 file changed, 4 insertions(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml b/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml
> > > > index 1ea60dff98d5..a8eaa1f18de5 100644
> > > > --- a/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml
> > > > +++ b/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml
> > > > @@ -33,6 +33,10 @@ properties:
> > > >      description:
> > > >        Analog supply voltage (AVDD).
> > > >
> > > > +  vsup-supply:
> > > > +    description:
> > > > +      Supply voltage for the on-chip regulator (VSUP).
> > > > +
> > > >    clock-frequency:
> > > >      description:
> > > >        Controls the SCK bit-bang timing. The value is used to derive the  
> > >  
> >  
>