linux-kernel - Re: [PATCH v3 00/10] gpio: sysfs: add a per-chip export/unexport attribute pair

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Message-ID: <CAMuHMdVFURtVovo4xUddULjchzK2Qae+ePHA3VKBeBo700a=gg@mail.gmail.com>
Date: Wed, 2 Jul 2025 14:05:15 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Kent Gibson <warthog618@...il.com>
Cc: Bartosz Golaszewski <brgl@...ev.pl>, Jan Lübbe <jlu@...gutronix.de>, 
	Andy Shevchenko <andriy.shevchenko@...el.com>, Ahmad Fatoum <a.fatoum@...gutronix.de>, 
	Marek Vasut <marex@...x.de>, Linus Walleij <linus.walleij@...aro.org>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3 00/10] gpio: sysfs: add a per-chip export/unexport
 attribute pair

On Wed, 2 Jul 2025 at 13:01, Kent Gibson <warthog618@...il.com> wrote:
> On Wed, Jul 02, 2025 at 12:28:01PM +0200, Bartosz Golaszewski wrote:
> > On Wed, Jul 2, 2025 at 12:12 PM Kent Gibson <warthog618@...il.com> wrote:
> > >
> > > >
> > > > I tend to not interpret it as adding new features. We really just
> > > > *move* what exists under a slightly different path when you think
> > > > about it.
> > > >
> > > > So what are you suggesting, remove the `edge` attribute and polling
> > > > features from the new `value` attribute?
> > > >
> > >
> > > Exactly. I'm not suggesting ANY changes to the old sysfs, only your new
> > > non-global numbering version.  The idea being don't port everything over
> > > from the old sysfs - just the core feature set that non-cdev users need.
> > >
> >
> > I mean, if someone shows up saying they need this or that from the old
> > sysfs and without they won't switch, we can always add it back I
> > guess... Much easier than removing something that's carved in stone.
>
> Exactly - expect to be supporting whatever goes in now forever.
>
> > Anything else should go away? `active_low`?
> >
>
> I don't personally see any value in 'active_low' in the sysfs API if you
> drop edges. It is easy enough to flip values as necessary in userspace.
> (From time to time I think it should've been dropped from cdev in v2 but, as
> above, it is carved in stone now so oh well...)

IMHO active_low is only really useful if you have some hardware
description that provides it, at which point you may be better off
having a real Linux
driver for the thing connected to the GPIO...

People who mess with GPIO /sysfs better know their hardware,
so they should be aware of the polarity.

>From my toolbox:
  - For pcf857x (which is pseudo-bi-directional), I usually just set
    direction to "in" (pulled high) or "out" (driven low),
  - For everything else, switching direction to "out" is ill-defined,
    so I do not write to ".../value", but set direction and value
    together by writing "high" or "low" to ".../direction",
  - For reading, I do use ".../value", of course.

My 0.02€...

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