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

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Date:   Wed, 30 Sep 2020 12:47:14 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Trent Piepho <tpiepho@...il.com>
Cc:     Drew Fustini <drew@...gleboard.org>,
        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>,
        Christina Quast <cquast@...overdisplays.com>
Subject: Re: [PATCH] ARM: dts: document pinctrl-single,pins when
 #pinctrl-cells = 2

* Trent Piepho <tpiepho@...il.com> [200930 09:34]:
> On Wed, Sep 30, 2020 at 2:15 AM Tony Lindgren <tony@...mide.com> wrote:
> >
> > * Trent Piepho <tpiepho@...il.com> [200930 08:35]:
> > > The closest thing would be the generic pin config type bindings, which
> > > go in the pinctrl driver's nodes, and look like this:
> > > &am335x_pinmux {
> > >     pinctrl_yoyo_reset: yoyogrp {
> > >         pins = "foo";
> > >         function = "gpio";
> > >         bias-pull-up;
> > >     };
> > > };
> >
> > There's a bit of a dtb size and boot time issue for adding properties
> > for each pin where that needs to be done for several hundred pins :)
> 
> pins is list, multiple pins can be specified at once.  Otherwise the
> property name would be "pin" and not "pins"  There's also a groups
> property to refer to multiple pins at once, e.g.
> 
> arch/mips/boot/dts/ingenic/ci20.dts-    pins_mmc1: mmc1 {
> arch/mips/boot/dts/ingenic/ci20.dts-            function = "mmc1";
> arch/mips/boot/dts/ingenic/ci20.dts:            groups =
> "mmc1-1bit-d", "mmc1-4bit-d";
> arch/mips/boot/dts/ingenic/ci20.dts-            bias-disable;
> arch/mips/boot/dts/ingenic/ci20.dts-    };
> 
> arch/mips/boot/dts/pic32/pic32mzda_sk.dts-      user_leds_s0: user_leds_s0 {
> arch/mips/boot/dts/pic32/pic32mzda_sk.dts:              pins = "H0", "H1", "H2";
> arch/mips/boot/dts/pic32/pic32mzda_sk.dts-              output-low;
> arch/mips/boot/dts/pic32/pic32mzda_sk.dts-              microchip,digital;
> arch/mips/boot/dts/pic32/pic32mzda_sk.dts-      };

Right.

> > > Is "some additional property for specifying generic conf flags"
> > > different from the existing pinctrl-single,bias-pullup, etc.
> > > properties?  Because splitting the data cell into two parts doesn't
> > > make any difference to those.
> >
> > So with an interrupt style binding with generic pinconf flags we can
> > leave out the parsing of multiple properties for each pin. Sure the
> > pin is only referenced by the controller like you pointed out but the
> > pinconf flags could be generic.
> 
> Where do these flags go?  In pinctrl-single,pins?  Like:
> 
> pinctrl-single,pins = <AM335X_PIN_MDC MUX_MODE7 PIN_INPUT_PULLUP>;
> 
> But PIN_INPUT_PULLUP is a generic flag?  Which is translated into the
> proper value by??

Yes that's what I was thinking, something like this with generic flags:

pinctrl-single,pins = <AM335X_PIN_MDC (PIN_INPUT | PIN_PULLUP) MUX_MODE7>;

> Or are you talking about replacing the existing pinctrl-0,
> pinctrl-names properties with a totally different system that looks
> more like gpio and interrupt handles?

That would be even better :) Might be just too much to deal with..

In any case the parser code could already be generic if we had generic
flags based on #pinctrl-cells.

Regards,

Tony