linux-kernel - Re: [PATCH 2/4] dt-bindings: pinctrl: Document nuvoton ma35d1 pin control

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Message-ID: <CACRpkdaiihOex19SavWwC+S8o5qp=F=XMNm9+UXh=q2nVbOFkA@mail.gmail.com>
Date:   Wed, 18 Oct 2023 10:18:07 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Jacky Huang <ychuang570808@...il.com>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        p.zabel@...gutronix.de, j.neuschaefer@....net,
        linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        schung@...oton.com, Jacky Huang <ychuang3@...oton.com>
Subject: Re: [PATCH 2/4] dt-bindings: pinctrl: Document nuvoton ma35d1 pin control

On Mon, Oct 16, 2023 at 9:52 PM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:

> > I noticed that 'xlnx,zynq-pinctrl.yaml' and 'xlnx,zynq-pinctrl.yaml' use
> > 'power source' to specify the output voltage.  Should I follow their
> > approach or define a vendor-specific one?
>
> Maybe Rob or Linus have here some recommendation, but I would suggest to
> go either with rtd1319d-pinctrl.yaml approach or add a generic property
> to pincfg-node expressed in real units like "io-microvolt".
>
> Rob, Linus, any ideas for generic property replacing register-specific
> power-source?

The existing power-source is generally used to select between (usually
two) different chip-internal power rails, such as 1.8V and 3.3V.
The format is a driver-specific enumerator.

We *could* just patch the documentation for power-source to
say that microvolts is the preferred format but legacy users may
be using a custom enumerator.

io-microvolt seems like a more long-term viable option if a wider
range of voltages are to be supported so I'm happy with that if the
DT folks think it's nicer. However notice that the power-source
property is already being hard-coded into things such as SCMI
and ACPI so it's not like it will ever be replaced by io-microvolt
and phased out as far as Linux is concerned. Not the next 50
years at least.

Yours,
Linus Walleij