linux-kernel - Re: [RFC PATCH v2] pinctrl: add helper to expose pinctrl state in debugfs

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Date:   Wed, 20 Jan 2021 19:19:10 -0800
From:   Drew Fustini <drew@...gleboard.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Pantelis Antoniou <pantelis.antoniou@...aro.org>,
        Pantelis Antoniou <pantelis.antoniou@...il.com>,
        Jason Kridner <jkridner@...gleboard.org>,
        Robert Nelson <robertcnelson@...gleboard.org>
Subject: Re: [RFC PATCH v2] pinctrl: add helper to expose pinctrl state in
 debugfs

On Mon, Jan 11, 2021 at 12:03:18PM +0200, Tony Lindgren wrote:
> Hi,
> 
> * Linus Walleij <linus.walleij@...aro.org> [210109 21:14]:
> > On Sat, Jan 9, 2021 at 3:55 AM Drew Fustini <drew@...gleboard.org> wrote:
> > 
> > > I discussed my use case and this patch on #armlinux earlier this week
> > > and Alexandre Belloni suggested looking at the pinmux-pins debugfs file.
> > 
> > This sounds reasonable.
> > 
> > > This made me think that a possible solution could be to define a store
> > > function for pinmux-pins to handle something like "<pin#> <function#>".
> > > I believe the ability to activate a pin function (or pin group) from
> > > userspace would satisfy our beagleboard.org use-case.
> > >
> > > Does that seem like a reasonable approach?
> > 
> > This sounds like a good approach.
> 
> Makes sense to me too.
> 
> We may want to make it into a proper sysfs interface eventually to not
> require debugfs be enabled in .config. But that's another set of patches,
> certainly makes sense to first enable it for debugfs.
> 
> Regards,
> 
> Tony

I have added a debugfs file "pinmux-set" to pinmux.c. This allows
"<function-number> <group-number>" to be written into that file. The
function pinmux_set_write() calls ops->set_mux() with fsel and gsel.

I'll post an RFC with the code, but I am wondering if it would better
to take the function as a name and then lookup the function number
(fsel)?

thanks,
drew