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

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Message-ID: <20200917092004.GA2468349@x1>
Date:   Thu, 17 Sep 2020 11:20:04 +0200
From:   Drew Fustini <drew@...gleboard.org>
To:     Trent Piepho <tpiepho@...il.com>
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 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.

> 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.


thanks,
drew

[1] https://lore.kernel.org/linux-omap/20200527165122.GL37466@atomide.com/