linux-kernel - Re: [PATCH v3 1/3] dt-bindings: spi: add spi-rx-bus-channels peripheral property

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Date: Mon, 8 Jan 2024 11:15:31 -0600
From: David Lechner <dlechner@...libre.com>
To: Mark Brown <broonie@...nel.org>
Cc: Jonathan Cameron <jic23@...nel.org>, linux-iio@...r.kernel.org, linux-spi@...r.kernel.org, 
	devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Michael Hennerich <michael.hennerich@...log.com>, Nuno Sá <nuno.sa@...log.com>, 
	Liam Girdwood <lgirdwood@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dt-bindings: spi: add spi-rx-bus-channels
 peripheral property

On Mon, Jan 8, 2024 at 10:39 AM Mark Brown <broonie@...nel.org> wrote:
>
> On Sun, Jan 07, 2024 at 05:02:56PM -0600, David Lechner wrote:
> > On Sun, Jan 7, 2024 at 3:27 PM Mark Brown <broonie@...nel.org> wrote:
>
> > > This makes no sense to me without a corresponding change in the SPI core
> > > and possibly controller support, though I guess you could do data
> > > manging to rewrite from a normal parallel SPI to this for a pure
> > > software implementation.  I also see nothing in the driver that even
> > > attempts to parse this so I can't see how it could possibly work.
>
> > We currently don't have a controller that supports this. This is just
> > an attempt to make a complete binding for a peripheral according to
> > [2] which says:
>
> ...
>
> > So, will DT maintainers accept an incomplete binding for the
> > peripheral? Or will you reconsider this without SPI core support if I
> > can explain it better? It doesn't seem like a reasonable request to
> > expect us to spend time developing software that we don't need at this
> > time just to get a complete DT binding accepted for a feature that
> > isn't being used.
>
> I don't think it's sensible to try to make a binding for this without
> having actually tried to put a system together that uses it and made
> sure that everything is joined up properly, the thing about complete
> bindings is more for things that are handle turning than for things that
> are substantial new features in subsystems.

We do have plans to eventually implement such a feature in an
FPGA-based SPI controller, so if we need to wait until then for the
binding, then we can do that. But it would be really nice if we could
find a way forward for the IIO driver in this series without having to
wait for the resolution of new SPI controller feature for the complete
DT bindings.

DT/IIO maintainers, if I resubmit this series with the
`spi-rx-bus-channels` parts removed from the iio/adc/adi,ad7380.yaml
bindings, would that be acceptable? (Also resubmitting without this
patch of course.)