Re: [PATCH v5 01/11] dt-bindings: iio: adc: Add AD4170

[Marcelo Schmitt <marcelo.schmitt1@gmail.com>]

On 06/16, Conor Dooley wrote:
> On Tue, Jun 10, 2025 at 05:31:04PM -0300, Marcelo Schmitt wrote:
> > Add device tree documentation for AD4170 and similar sigma-delta ADCs.
> > The AD4170 is a 24-bit, multichannel, sigma-delta ADC.
> > 
> > Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
> > ---
...
> > +
> > +$defs:
> > +  reference-buffer:
> > +    description: |
> > +      Enable precharge buffer, full buffer, or skip reference buffering of
> > +      the positive/negative voltage reference. Because the output impedance
> > +      of the source driving the voltage reference inputs may be dynamic,
> > +      resistive/capacitive combinations of those inputs can cause DC gain
> > +      errors if the reference inputs go unbuffered into the ADC. Enable
> > +      reference buffering if the provided reference source has dynamic high
> > +      impedance output. Note the absolute voltage allowed on REFINn+ and REFINn-
> > +      inputs is from AVSS - 50 mV to AVDD + 50 mV when the reference buffers are
> > +      disabled but narrows to AVSS to AVDD when reference buffering is enabled
> > +      or in precharge mode. The valid options for this property are:
> > +      0: Reference precharge buffer.
> > +      1: Full reference buffering.
> > +      2: Bypass reference buffers (buffering disabled).
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    enum: [0, 1, 2]
> > +    default: 1
> 
> Why make this property a uint32, rather than a string where you can use
> something like "precharge", "full" and "bypass" (or "disabled")? The
> next similar device could use something slightly different then the
> binding becomes pretty clunky.

Oh, good point. Will make it string type (if going to keep the property).

> Can you explain why this is a dt property rather than something
> adjustable at runtime?

The reference buffer configuration affects the allowed absolute maximum input
ratings of voltage reference supplies. Some bindings (adi,ad7192, adi,ad4130,
adi,ad7124) have dt properties for buffering of analog inputs and adi,max11410
has a prop for reference buffering. It looked like adi,ad4170 having a dt prop
for reference buf would make it more consistent with other bindings. Though, I'm
fine with dropping ad4170 reference buffer props if that would be better.

Thanks,
Marcelo