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

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Message-ID: <20250702124231.GA55860@rigel>
Date: Wed, 2 Jul 2025 20:42:31 +0800
From: Kent Gibson <warthog618@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Bartosz Golaszewski <brgl@...ev.pl>,
	Jan Lübbe <jlu@...gutronix.de>,
	Ahmad Fatoum <a.fatoum@...gutronix.de>, Marek Vasut <marex@...x.de>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	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, Jul 02, 2025 at 02:59:43PM +0300, Andy Shevchenko wrote:
> On Wed, Jul 02, 2025 at 07:01:27PM +0800, Kent Gibson 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.
>
> +1, this is my biggest worries about the interfaces proposed by this series.
>
> > > 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...)
>
> But in cdev case this is different. Active-low state is needed to be
> HW independent. For sysfs I agree as it's _already_ HW *dependent*
> (due to global number space in use at bare minumum).
>

As Geert pointed out, userspace needs to set the 'active_low' itself, so
it isn't really providing hardware independence.

The issue isn't whether the logical/physical mapping should exist, but
whether there is any benefit having it baked into the API.
It could've been added in userspace instead and made the uAPI a tad simpler
with one less source of confusion.

Cheers,
Kent.