linux-kernel - Re: [PATCH v4 1/2] dt-bindings: gpio-mux-input: add documentation

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Date:   Tue, 1 Jun 2021 12:44:18 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Mauri Sandberg <maukka@....kapsi.fi>
Cc:     Mauri Sandberg <sandberg@...lfence.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Drew Fustini <drew@...gleboard.org>
Subject: Re: [PATCH v4 1/2] dt-bindings: gpio-mux-input: add documentation

On Sun, May 30, 2021 at 6:16 PM Mauri Sandberg <maukka@....kapsi.fi> wrote:

> Add documentation for a general GPIO multiplexer.
>
> Signed-off-by: Mauri Sandberg <maukka@....kapsi.fi>
> Tested-by: Drew Fustini <drew@...gleboard.org>
> Reviewed-by: Drew Fustini <drew@...gleboard.org>

After some thinking I realized these bindings should not
be restricted to just input. There exist electronic constructions
such as open drain that would make it possible to mux also
outputs.

>  .../bindings/gpio/gpio-mux-input.yaml         | 75 +++++++++++++++++++

Rename it just gpio-mux.yaml

> +$id: http://devicetree.org/schemas/gpio/gpio-mux-input.yaml#

Also here

> +title: Generic GPIO input multiplexer

Generic GPIO multiplexer

> +description: |
> +  A generic GPIO based input multiplexer

Not just input

> +  This driver uses a mux-controller to drive the multiplexer and has a single
> +  output pin for reading the inputs to the mux.

Make this clearer and do not mention "driver".
Here is a suggestion:

This hardware construction multiplexes (cascades) several GPIO
lines from one-to-many using a software controlled multiplexer.
The most common use case is probably reading several inputs
by switching the multiplexer over several input lines, which in
practice works well since input lines has high impedance.

Constructions with multiplexed outputs are also possible using
open drain electronics.

> +  For GPIO consumer documentation see gpio.txt.

No need to mention this I think, not your problem :D

> +  pin-gpios:

I still want this renamed like in my previous mail.

Hope all is clear!

Yours,
Linus Walleij