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

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Hi,

Am Donnerstag, 2. Februar 2023, 18:10:52 CET schrieb Jonathan Cameron:
> On Wed, 1 Feb 2023 13:13:43 +0100
> 
> Marco Felsch <m.felsch@pengutronix.de> wrote:
> > Hi Alexander,
> > 
> > On 23-01-31, Alexander Stein wrote:
> > > Hi Marco,
> > > 
> > > thanks for the feedback.
> > > 
> > > Am Dienstag, 31. Januar 2023, 11:48:16 CET schrieb Marco Felsch:
> > > > Hi Alexander,
> > > > 
> > > > On 23-01-31, Alexander Stein 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@ew.tq-group.com>
> > > > > ---
> > > > > 
> > > > >  .../devicetree/bindings/iio/adc/nxp,imx8qxp-adc.yaml          | 4
> > > > >  ++++
> > > > >  1 file changed, 4 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..879768af0303 100644
> > > > > --- a/Documentation/devicetree/bindings/iio/adc/nxp,imx8qxp-adc.yaml
> > > > > +++ b/Documentation/devicetree/bindings/iio/adc/nxp,imx8qxp-adc.yaml
> > > > > 
> > > > > @@ -39,6 +39,9 @@ properties:
> > > > >    power-domains:
> > > > >      maxItems: 1
> > > > > 
> > > > > +  vref-supply:
> > > > > +    description: External ADC reference voltage supply on VREFH
> > > > > pad.
> > > > 
> > > > Please add it to the list of required properties, we can remove it as
> > > > soon as the driver has support for the internal reference voltages.
> > > 
> > > I was thinking in doing so before as well. But DT describes the
> > > hardware, and this ADC apparently would be functioning without a
> > > reference voltage on that pad, using a different one. What the driver
> > > actual does is a different matter.> 
> > I have also thought about it first but than I checked the RM which says
> > that "multi-reference selection" is chip dependent.

Nice for pointing this out. I wasn't aware that there are differences.

> Oh goody. So is it detectable?

That's my problem. I didn't find any source of information which chips do 
support multiple references and which don't.
Marco, do you have some information on this?

> If we are going to stick to a single compatible rather than adding them for
> the variants with and without this feature, should probably add a note at
> least to say it is required for some parts.

That's a good idea. I'm okay with that, until there is more information 
available.

Best regards
Alexander

> Also, link if public would be good for purposes of discussion as my google
> fu didn't find relevant doc. (assuming it's public)
> 
> 
> Jonathan
> 
> > Regards,
> > 
> >   Marco
> >   
> > > Best regards,
> > > Alexander
> > > 
> > > > Regards,
> > > > 
> > > >   Marco
> > > >   
> > > > > +
> > > > > 
> > > > >    "#io-channel-cells":
> > > > >      const: 1
> > > > > 
> > > > > @@ -72,6 +75,7 @@ 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>;
> > > > >          
> > > > >          };
> > > > >      
> > > > >      };