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Date:   Wed, 19 May 2021 21:17:33 -0700
From:   Drew Fustini <drew@beagleboard.org>
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Dario Binacchi <dariobin@libero.it>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        Vladimir Zapolskiy <vz@mleia.com>
Subject: Re: [PATCH 1/2] pinctrl: core: configure pinmux from pins debug file
Message-ID: <20210520041733.GA3269241@x1>
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On Wed, May 19, 2021 at 02:27:38PM +0300, Andy Shevchenko wrote:
> On Wed, May 19, 2021 at 1:02 PM Drew Fustini <drew@beagleboard.org> wrote:
> > On Tue, May 18, 2021 at 05:01:30PM +0300, Andy Shevchenko wrote:
> 
> ...
> 
> > Vladimir Zapolskiy wrote in e73339037f6b ("pinctrl: remove unused
> > 'pinconf-config' debugfs interface"):
> >
> >     Of course it might be possible to increase MAX_NAME_LEN, and then add
> >     .pin_config_dbg_parse_modify callbacks to the drivers, but the whole
> >     idea of such a limited debug option looks inviable. A more flexible
> >     way to functionally substitute the original approach is to implicitly
> >     or explicitly use pinctrl_select_state() function whenever needed.
> >
> > This makes me think it is not a good idea to bring back pinconf-config.
> > The pinmux-select debugfs file that I add added in commit 6199f6becc86
> > ("pinctrl: pinmux: Add pinmux-select debugfs file") provides a method to
> > activate a pin function and pin group which I think provides the same
> > capability as long as the possible pin functions are described in dts.
> 
> The problem is that the pinctrl_select_state() is very limited and has
> no clear meanings of the states. Only few are defined and still
> unclear. What does `sleep` or `standby` or whatever mean? It may be
> quite different to the device in question. Basically what we need is
> to say we want this device ('function') to appear on this group of
> pins ('group'). And pinctrl_select_state() can't fulfill this simple
> task :-(
> 
> If we look at the ACPI case it makes that API completely out of useful
> context (it can be used due to above and some kind of layering
> violations, like PM vs. pin control).
> 
> Since above is the debugfs interface we may return it for the certain
> task, i.e. printing current function / group choice(s) (if it's not
> done by other means) and allow to switch it desired function/group
> (that's what Dario tries to achieve AFAIU).

A write to the pinmux-select debugfs file will call pinmux_select() in
drivers/pinctrl/pinmux.c which, after some validation checks, will call
pmxops->set_mux() with function selector and group selector as
arguments.  For pinctrl-single, this will invoke pcs_set_mux() which
will ultimately set the mux mode bits in the register for each pin in
that function.

IS that useful for pin controllers in ACPI systems as well?

thanks,
drew