Re: [PATCH 1/5] dt-bindings: iio: dac: ti,dac5571: Add DAC081C081 support

[Jonathan Cameron]

On 25 March 2024 22:23:08 GMT, Laurent Pinchart <laurent.pinchart at ideasonboard.com> wrote:
>On Mon, Mar 25, 2024 at 10:56:44PM +0200, Laurent Pinchart wrote:
>> On Mon, Mar 25, 2024 at 08:48:57PM +0000, Jonathan Cameron wrote:
>> > On Mon, 25 Mar 2024 22:32:41 +0200 Laurent Pinchart wrote:
>> > 
>> > > The DAC081C081 is a TI DAC whose software interface is compatible with
>> > > the DAC5571. It is the 8-bit version of the DAC121C081, already
>> > > supported by the DAC5571 bindings. Extends the bindings to support this
>> > > chip.
>> > > 
>> > > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
>> > 
>> > Hi Laurent,
>> > 
>> > Given it's a part number where no one is going to guess it is compatible
>> > with the DAC5571 and that we don't have a history of fallback compatibles
>> > I'm fine with this change, but just wanted to ask is a fallback compatible
>> > useful to you to run with older kernels?
>> > 
>> > I should have noticed when Peter added the dac121c081. If we add a fallback
>> > should do that one as well.
>> 
>> I've indeed noticed that there should have been a fallback for
>> dac121c081, but didn't stop to ponder why that wasn't the case, and just
>> went along with the flow :-) I agree a fallback could be useful, which
>> would then allow dropping patch 2/5 from this series (*). I can do so if
>> you prefer.
>
>And in that case, should I first introduce support in the bindings for
>"ti,dac121c081", "ti,dac7571" and deprecate usage of "ti,dac121c081"
>alone ?

Yes. Not sure if we need an explicit binding entry for deprecated version...

>
>> * This is not entirely true. While the DAC1081C081 is largely compatible
>> with the DAC5573, they have different values for one of the power-down
>> resistors (2.5kΩ instead of 1kΩ if I recall correctly). To be completely
>> accurate, the driver should report that. We could still use the fallback
>> compatible, reporting the wrong power-down resistor value.
>> 
>> > > ---
>> > >  Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml | 1 +
>> > >  1 file changed, 1 insertion(+)
>> > > 
>> > > diff --git a/Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml b/Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml
>> > > index 79da0323c327..e59db861e2eb 100644
>> > > --- a/Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml
>> > > +++ b/Documentation/devicetree/bindings/iio/dac/ti,dac5571.yaml
>> > > @@ -21,6 +21,7 @@ properties:
>> > >        - ti,dac5573
>> > >        - ti,dac6573
>> > >        - ti,dac7573
>> > > +      - ti,dac081c081
>> > >        - ti,dac121c081
>> > >  
>> > >    reg:
>