linux-kernel - Re: [PATCH v9 2/4] pinctrl: pinmux: Add pinmux-select debugfs file

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Date:   Sat, 13 Mar 2021 19:47:24 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Drew Fustini <drew@...gleboard.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tony Lindgren <tony@...mide.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Jason Kridner <jkridner@...gleboard.org>,
        Robert Nelson <robertcnelson@...gleboard.org>,
        Joe Perches <joe@...ches.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH v9 2/4] pinctrl: pinmux: Add pinmux-select debugfs file

Hi Alexandre,

On Sat, Mar 13, 2021 at 10:28 AM Alexandre Belloni
<alexandre.belloni@...tlin.com> wrote:
> On 12/03/2021 14:57:54+0100, Enrico Weigelt, metux IT consult wrote:
> > On 02.03.21 06:30, Drew Fustini wrote:
> > > Add "pinmux-select" to debugfs which will activate a pin function for a
> > > given pin group:
> > >
> > >    echo "<group-name function-name>" > pinmux-select
> > >
> > > The write operation pinmux_select() handles this by checking that the
> > > names map to valid selectors and then calling ops->set_mux().
> >
> > I've already been playing with similar idea, but for external muxes.
> > For example, some boards have multiple SIM slots that can be switched
> > via some gpio pin.
> >
> > Not sure whether traditional pinmux would be a good match for that.
>
> If you want to be able to use both, then I guess gpio-mux is what you
> are looking for. Obviously, it will also require support in the bus
> core. On what bus are those SIMs? (I guess the answer will be UART and
> then unfortunately UARTs are not represented as busses).

We do have support for devices connected to UARTs.
See patternProperties in Documentation/devicetree/bindings/serial/serial.yaml.
Or do you mean something different?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds