Re: [PATCH v2 1/1] dt-bindings: iio: imx8qxp-adc: add missing vref-supply

[Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>]

Am Sonntag, 30. April 2023, 19:15:58 CEST schrieb Jonathan Cameron:
> On Mon, 24 Apr 2023 11:23:12 +0200
> 
> Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx> wrote:
> > Although this property is used right now for IIO_CHAN_INFO_SCALE,
> > this ADC has two internal reference voltages, which the driver currently
> > doesn't make use of.
> > 
> > Fixes: db73419d8c06 ("dt-bindings: iio: adc: Add binding documentation for
> > NXP IMX8QXP ADC") Signed-off-by: Alexander Stein
> > <alexander.stein@xxxxxxxxxxxxxxx>
> 
> Interesting that we are talking her only about vrefh, what about vrefp?
> I guess the assumption is that will be wired to 0V?

What's vrefp? The only other signal related to ADC is vrefl.

> The first reference I found didn't seem to imply that was necessarily the
> case. https://www.mouser.com/pdfDocs/IMX8QXPAEC.pdf

Assuming you are talking about vrefh and vrefl, how is this a problem? Even if 
vrefl is not 0V, the voltage difference is what the ADC uses as reference 
voltage, so this should be supplied in the DT then.

Best regards
Alexander

> Jonathan
> 
> > ---
> > Thanks for your inputs. This improved descritpion should make it clear
> > that this property is only about the external reference voltage, not
> > about the optional, internal voltages.
> > 
> > Changes in v2:
> > * Improved commit message subject as suggested
> > * Add hint about feature flag regarding multiple, internal, reference
> > 
> >   voltages
> >  
> >  .../devicetree/bindings/iio/adc/nxp,imx8qxp-adc.yaml       | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git
> > a/Documentation/devicetree/bindings/iio/adc/nxp,imx8qxp-adc.yaml
> > b/Documentation/devicetree/bindings/iio/adc/nxp,imx8qxp-adc.yaml index
> > 63369ba388e4..878e67054d7c 100644
> > --- a/Documentation/devicetree/bindings/iio/adc/nxp,imx8qxp-adc.yaml
> > +++ b/Documentation/devicetree/bindings/iio/adc/nxp,imx8qxp-adc.yaml
> > 
> > @@ -39,6 +39,12 @@ properties:
> >    power-domains:
> >      maxItems: 1
> > 
> > +  vref-supply:
> > +    description: |
> > +      External ADC reference voltage supply on VREFH pad. If VERID[MVI]
> > is
> > +      set, there are additional, internal reference voltages selectable.
> > +      VREFH1 is always from VREFH pad.
> > +
> > 
> >    "#io-channel-cells":
> >      const: 1
> > 
> > @@ -72,6 +78,7 @@ examples:
> >              assigned-clocks = <&clk IMX_SC_R_ADC_0>;
> >              assigned-clock-rates = <24000000>;
> >              power-domains = <&pd IMX_SC_R_ADC_0>;
> > 
> > +            vref-supply = <&reg_1v8>;
> > 
> >              #io-channel-cells = <1>;
> >          
> >          };
> >      
> >      };


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