Re: [RFC PATCH] dt-bindings: iio: adc: use spi-peripheral-props.yaml

[Rob Herring <robh@kernel.org>]

On Sat, Jul 16, 2022 at 07:26:04PM +0100, Jonathan Cameron wrote:
> On Fri, 15 Jul 2022 11:53:02 +0200
> Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> wrote:
> 
> > Instead of listing directly properties typical for SPI peripherals,
> > reference the spi-peripheral-props.yaml schema.  This allows using all
> > properties typical for SPI-connected devices, even these which device
> > bindings author did not tried yet.
> > 
> > Remove the spi-* properties which now come via spi-peripheral-props.yaml
> > schema, except for the cases when device schema adds some constraints
> > like maximum frequency.
> > 
> > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> > 
> > ---
> > 
> > This is an RFC with only some files changed, as I am still not sure of
> > benefits for typical case - device node has just spi-max-frequency and
> > nothing more.  I still find useful to reference the schema, but maybe I
> > am missing something?
> > 
> > Before doing wide-tree cleanup like this, I would be happy to receive
> > some feedback whether this makes sense.
> 
> Hi Krzysztof,
> 
> This has the side effect of allowing spi-cpol / spi-cpha for devices
> where they weren't previously allowed by the binding.  A typical device
> only supports a subset of combinations of those.
> 
> I'm not clear whether these should always be allowed (e.g. allow for inverters
> etc in the path) or whether we should be enforcing the "correct"
> settings for devices assuming they are directly connected.
> 
> Currently we have a bunch of bindings that are documenting the allowed
> flexibility - including cases where only particular combinations of these
> settings are allowed.
> 
> So we could either:
> 1) Note that we've been doing it wrong and the binding should not enforce
>    these constraints so remove them.

I'd lean towards this.

> 2) Add explicit spi-cpol: false statements etc the drivers where they
>    are not allowed.

3) Drop spi-cpol / spi-cpha from spi-peripheral-props.yaml. It's purpose 
is to collect all possible SPI controller properties that are per child 
node. Whereas we've said spi-cpol / spi-cpha are device specific 
properties.

Rob