linux-kernel - Re: [PATCH v2] ARM: dts: am335x-pocketbeagle: set default mux for gpio pins

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Date:   Tue, 30 Jun 2020 23:42:31 +0200
From:   Drew Fustini <drew@...gleboard.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Rob Herring <robh+dt@...nel.org>, bcousson@...libre.com,
        linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Jason Kridner <jkridner@...gleboard.org>,
        Robert Nelson <robertcnelson@...il.com>,
        "H . Nikolaus Schaller" <hns@...delico.com>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v2] ARM: dts: am335x-pocketbeagle: set default mux for
 gpio pins

On Tue, Jun 30, 2020 at 02:34:23PM -0700, Tony Lindgren wrote:
> * Drew Fustini <drew@...gleboard.org> [200630 21:32]:
> > On Tue, Jun 30, 2020 at 11:20:37AM -0700, Tony Lindgren wrote:
> ...
> > > > > Needing to change the dts does not sound good to me.. But maybe you mean
> > > > > this is needed until the gpio-omap and pinctrl-single patches are merged?
> > > >
> > > > I agree that I would like for userspace to be able to do run-time
> > > > changes.  However, I think something would need to be added to the
> > > > pinconf support in pinctrl-single for that to be possible.  There are
> > > > bias properties but non for receiver enable.
> > > > 
> > > > Does it seem sensible to add that?
> > > 
> > > Well let's see with Linus W says. To me it seems this might be a good
> > > reason to allow a sysfs interface to change the pinctrl if we don't
> > > have it yet? With the proper gpio line naming it should be quite simple
> > > to use too :)
> > 
> > I think if pinctrl-single allowed mux to be set through debugfs that
> > could be one solution to the use case of users prototyping with a
> > beaglebone.  Maybe that could be acceptable?
> 
> I think this should not depend on debugfs though, it should be a
> generic interface.

Ok, thanks.  I'm trying to imagine a solution as there no existing
pinctrl uAPI.  gpiod uAPI has gained some pinctrl functionality with
the work that Kent Gibson has been doing beyond just bias flags.

Do you think trying to plumb this through gpio-omap is a reasonable
approach?

thanks,
drew