linux-kernel - Re: [PATCH] ARM: dts: document pinctrl-single,pins when #pinctrl-cells = 2

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Message-ID: <CA+7tXii8rwBexgAHeqYsvBywhWLmk-Hf5_VWUU5bQkBREeFcSA@mail.gmail.com>
Date:   Thu, 17 Sep 2020 02:03:46 -0700
From:   Trent Piepho <tpiepho@...il.com>
To:     Drew Fustini <drew@...gleboard.org>
Cc:     Tony Lindgren <tony@...mide.com>, Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jason Kridner <jkridner@...gleboard.org>,
        Robert Nelson <robertcnelson@...il.com>,
        linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-gpio <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH] ARM: dts: document pinctrl-single,pins when
 #pinctrl-cells = 2

On Mon, Sep 14, 2020 at 3:44 AM Drew Fustini <drew@...gleboard.org> wrote:
>
> +
> +When #pinctrl-cells = 2, then setting a pin for a device could be done with:
> +
> +       pinctrl-single,pins = <0xdc 0x30 0x07>;
> +
> +Where 0x30 is the pin configuration value and 0x07 is the pin mux mode value.
> +See the device example and static board pins example below for more information.

Pin configuration and mux mode don't mean anything in pinctrl-single.
On another machine, mux mode might not be programmed this way or even
exist.  Or the location of bits would probably be different, and this
would seem to imply the 0x07 would get shifted to the correct location
for where the pin mux setting was on that machine's pinctrl registers.

It seems like it would be better to explain the values are ORed together.

What is the purpose of this change anyway?  It seems like in the end
it just does what it did before.  The data is now split into two cells
in the device tree, but why?