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

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Message-ID: <CA+7tXihwHbcuxZ10jGZrQkET9+Dbs31SfsYDt_6XB+-JM99gqA@mail.gmail.com>
Date:   Thu, 17 Sep 2020 03:00:36 -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 Thu, Sep 17, 2020 at 2:20 AM Drew Fustini <drew@...gleboard.org> wrote:
>
> On Thu, Sep 17, 2020 at 02:03:46AM -0700, Trent Piepho wrote:
> > 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.
>
> I descirbed it as seoerate values as I did not want to prescribe what
> the pcs driver would do with those values.  But, yes, it is a just an OR
> operation, so I could change the language to reflect tat.

If you don't say what the pinctrl-single driver does with the values,
how would anyone know how to use it?

> > 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?
>
> These changes were a result of desire to seperate pinconf and pinmux.
> Tony raised the idea in a thread at the end of May [1].
>
> Tony wrote:
> > Only slightly related, but we should really eventually move omaps to use
> > #pinctrl-cells = <2> (or 3) instead of 1, and pass the pinconf seprately
> > from the mux mode. We already treat them separately with the new
> > AM33XX_PADCONF macro, so we'd only have to change one SoC at a time to
> > use updated #pinctrl-cells. But I think pinctrl-single might need some
> > changes before we can do that.

I still don't see what the goal is here.  Support generic pinconf?

Also note that while AM33XX_PADCONF() is changed, there is an in tree
board that doesn't use it, so it's broken now.  I found this change
when it broke my out of tree board, due to the dtsi change not being
reflected in my board's pinctrl values.