linux-kernel - Re: [PATCH 1/3] dt-bindings: spi: Add VIA/WonderMedia serial flash controller

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Message-ID: <87y0u1z3jk.fsf@bootlin.com>
Date: Mon, 09 Jun 2025 11:07:27 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Alexey Charkov <alchark@...il.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,  Rob Herring <robh@...nel.org>,
  Mark Brown <broonie@...nel.org>,  Krzysztof Kozlowski
 <krzk+dt@...nel.org>,  Conor Dooley <conor+dt@...nel.org>,  Tudor Ambarus
 <tudor.ambarus@...aro.org>,  Pratyush Yadav <pratyush@...nel.org>,
  Michael Walle <mwalle@...nel.org>,  Richard Weinberger <richard@....at>,
  Vignesh Raghavendra <vigneshr@...com>,  linux-spi@...r.kernel.org,
  devicetree@...r.kernel.org,  linux-kernel@...r.kernel.org,
  linux-mtd@...ts.infradead.org,  linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] dt-bindings: spi: Add VIA/WonderMedia serial flash
 controller

Hi Alexey,

>> > Happy to reference the spi-controller.yaml binding if so.
>>
>> SPI NOR flashes are still child devices of an SPI controller. You can
>> look at other examples - aren't they all using spi-controller? Why this
>> would be different? Unless you found some cases that are different, but
>> then which ones?
>
> No strong opinions here, and no expectation of any special treatment
> :) Just wanted to consult on what's most appropriate.
>
> My (subjective and perhaps unfounded) expectation when seeing
> something advertise itself as an SPI controller was that it would be a
> general purpose SPI master, to which one can e.g. connect an SPI
> driven LCD screen and get it to work with generic Linux SPI
> infrastructure - which would not be possible with this single-purpose
> NOR-only flash controller. Given that I don't know how flexible or
> restrictive other examples are in terms of driving arbitrary SPI
> devices, I thought it's better to just ask.
>
> What I'm getting from this exchange here is that I'd better use the
> spi-controller binding and respective node names regardless of the
> fact that this controller cannot drive arbitrary SPI devices beyond
> NOR flash (which, as I'm getting, is irrelevant after all).

Just for information, there are several SPI controllers which are
optimized for flash handling (not only NOR, though) and for that we have
a spi-mem layer which allows to reference a set of SPI memory "only"
callbacks. On the description side though, these controllers are like
all other SPI controllers, so the same controller bindings may apply.

Thanks,
Miquèl