linux-kernel - Re: [PATCH v2 2/9] dt-bindings: pincfg-node: Add property "skew-delay-direction"

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Message-ID: <CACRpkdZCKXYEegV1cK6X9A9k8ORLWweBQs40PWYuTof3JgcC2w@mail.gmail.com>
Date: Tue, 30 Sep 2025 14:23:25 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Antonio Borneo <antonio.borneo@...s.st.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Maxime Coquelin <mcoquelin.stm32@...il.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Bartosz Golaszewski <brgl@...ev.pl>, linux-gpio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org, 
	Christophe Roullier <christophe.roullier@...s.st.com>, 
	Fabien Dessenne <fabien.dessenne@...s.st.com>, Valentin Caron <valentin.caron@...s.st.com>
Subject: Re: [PATCH v2 2/9] dt-bindings: pincfg-node: Add property "skew-delay-direction"

Hi Antonio,

thanks for your patch!

And sorry that it takes so long for me to review it! :(

On Fri, Sep 5, 2025 at 3:56 PM Antonio Borneo
<antonio.borneo@...s.st.com> wrote:

> Add the property "skew-delay-direction" to specify on which pin's
> direction (either input, output or both) the value of the generic
> property 'skew-delay' applies.
> For backward compatibility, 'skew-delay' applies on both input and
> output directions when the new property is not present or has
> value '0'.
>
> Signed-off-by: Antonio Borneo <antonio.borneo@...s.st.com>
(...)
> +  skew-delay-direction:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [0, 1, 2]
> +    default: 0
> +    description: |
> +      0: skew-delay applies to both input and output directions
> +      1: skew-delay applies only to the output direction
> +      2: skew-delay applies only to the input direction

Unfortunately I don't think this will work, because skew-delay
has a value, and with this scheme we can only specify that we
want this value to affect both in/out, only in or only out.

What happens when someone want to configure different
skew delay for input and output?

I think it is better to add:

skew-delay-input = <u32>;
skew-delay-output = <u32>;

So the drivers that need this explicitly specified will need
to just define one of these instead.

If you want to be very determined, make the schema
not accept skew-delay if either skew-delay-input
or skew-delay-output is specified.

Yours,
Linus Walleij