linux-kernel - Re: [PATCH RFC/RFT 00/15] gpio: sysfs: add a per-chip export/unexport attribute pair

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Message-ID: <CAMRc=MdbYesiRDfvwSchZZ5jOnSRffS3JzUzQh++J1JZLwm1Wg@mail.gmail.com>
Date: Mon, 16 Jun 2025 14:27:06 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Ahmad Fatoum <a.fatoum@...gutronix.de>, Kent Gibson <warthog618@...il.com>, 
	Jan Lübbe <jlu@...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 RFC/RFT 00/15] gpio: sysfs: add a per-chip export/unexport
 attribute pair

On Fri, Jun 13, 2025 at 10:02 AM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
>
> Hi Bartosz,
>
> On Tue, 10 Jun 2025 at 16:38, Bartosz Golaszewski <brgl@...ev.pl> wrote:
> > Following our discussion[1], here's a proposal for extending the sysfs
> > interface with attributes not referring to GPIO lines by their global
> > numbers in a backward compatible way.
> >
> > Long story short: there is now a new class device for each GPIO chip.
> > It's called chipX where X is the ID of the device as per the driver
> > model and it lives next to the old gpiochipABC where ABC is the GPIO
> > base. Each new chip class device has a pair of export/unexport
> > attributes which work similarly to the global ones under /sys/class/gpio
> > but take hardware offsets within the chip as input, instead of the
> > global numbers. Finally, each exported line appears at the same time as
> > the global /sys/class/gpio/gpioABC as well as per-chip
> > /sys/class/gpio/chipX/gpioY sysfs group.
> >
> > First, there are some documentation updates, followed by a set of
> > updates to the sysfs code that's useful even without the new
> > functionality. Then the actual implementation of a parallel GPIO chip
> > entry not containing the base GPIO number in the name and the
> > corresponding sysfs attribute group for each exported line that lives
> > under the new chip class device. Finally: also allow to compile out the
> > legacy parts leaving only the new elements of the sysfs ABI.
> >
> > This series passes the compatibility tests I wrote while working on the
> > user-space compatibility layer for sysfs[2].
> >
> > [1] https://lore.kernel.org/all/CAMRc=McUCeZcU6co1aN54rTudo+JfPjjForu4iKQ5npwXk6GXA@mail.gmail.com/
> > [2] https://github.com/brgl/gpio-sysfs-compat-tests
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> Thanks for your series!
>
> I gave it a quick try, and it seems to work as expected, great!
>
> Given the /sys/class/gpio/chip* numbering is volatile, I expect
> script writers should use topological path names instead, .e.g.
> /sys/devices/platform/soc/e6052000.gpio/gpio/chip*/export and
> sys/devices/platform/soc/e6052000.gpio/gpio/chip*/gpio19
> (note the wildcards).
>

Or they can use the chip label like what they would do with the
character device. The relevant attribute is still there.

Bartosz