linux-kernel - Re: [PATCH v7 2/3] pinctrl: pinmux: Add pinmux-select debugfs file

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Date:   Sat, 20 Feb 2021 10:28:27 -0800
From:   Drew Fustini <drew@...gleboard.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     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>,
        Alexandre Belloni <alexandre.belloni@...tlin.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>
Subject: Re: [PATCH v7 2/3] pinctrl: pinmux: Add pinmux-select debugfs file

On Fri, Feb 19, 2021 at 10:06:51AM +0100, Geert Uytterhoeven wrote:
> Hi Drew,
> 
> On Wed, Feb 17, 2021 at 11:15 PM Drew Fustini <drew@...gleboard.org> wrote:
> > Add "pinmux-select" to debugfs which will activate a function and group:
> >
> >   echo "<function-name group-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().
> >
> > The existing "pinmux-functions" debugfs file lists the pin functions
> > registered for the pin controller. For example:
> >
> >   function: pinmux-uart0, groups = [ pinmux-uart0-pins ]
> >   function: pinmux-mmc0, groups = [ pinmux-mmc0-pins ]
> >   function: pinmux-mmc1, groups = [ pinmux-mmc1-pins ]
> >   function: pinmux-i2c0, groups = [ pinmux-i2c0-pins ]
> >   function: pinmux-i2c1, groups = [ pinmux-i2c1-pins ]
> >   function: pinmux-spi1, groups = [ pinmux-spi1-pins ]
> >
> > To activate function pinmux-i2c1 and group pinmux-i2c1-pins:
> >
> >   echo "pinmux-i2c1 pinmux-i2c1-pins" > pinmux-select
> >
> > Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
> > Reviewed-by: Tony Lindgren <tony@...mide.com>
> > Signed-off-by: Drew Fustini <drew@...gleboard.org>
> 
> Thanks for your patch!
> 
> On R-Car M2-W, which does not use pinctrl-single, I have:
> 
>     # cat pinmux-functions
>     ...
>     function 14: i2c2, groups = [ i2c2 i2c2_b i2c2_c i2c2_d ]
>     ...
>     function 51: ssi, groups = [ ssi0_data ssi0_data_b ssi0129_ctrl
> ssi0129_ctrl_b ssi1_data ssi1_data_b ssi1_ctrl ssi1_ctrl_b ssi2_data
> ssi2_ctrl ssi3_data ssi34_ctrl ssi4_data ssi4_ctrl ssi5_data ssi5_ctrl
> ssi6_data ssi6_ctrl ssi7_data ssi7_data_b ssi78_ctrl ssi78_ctrl_b
> ssi8_data ssi8_data_b ssi9_data ssi9_data_b ssi9_ctrl ssi9_ctrl_b ]
>     ...
> 
> On the Koelsch board:
> 
>     # cd /sys/kernel/debug/pinctrl/e6060000.pinctrl-sh-pfc/
>     # echo ssi ssi2_ctrl > pinmux-select # Configure i2c2 pins for ssi
>     # i2cdetect -y -a 2                  # Fails
>     # echo i2c2 i2c2 > pinmux-select     # Restore i2c2
>     # i2cdetect -y -a 2                  # Works again
> 
> The order of the 2 parameters looks a bit odd to me, as the operation
> configures the pins from "group" to be used for "function".
> See also arch/arm/boot/dts/r8a7791-koelsch.dts
> For the i2c2 example it's not that obvious, but for ssi it is.
> Might feel different for pinctrl-single, and perhaps I just need to get
> used to it ;-)

Thank you for comments and testing.

Regarding the order of "<function-name> <group-name>", I can change it
to "<group-name function-name>" if that seems more natural.

pinctrl-single does not actually use the group selector in pcs_set_mux()
so it essentially does not matter for pinctrl-single.

-Drew

> 
> Anyway:
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
> 
> 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