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

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Message-ID: <aGPrFnDxG4W7S9Ym@smile.fi.intel.com>
Date: Tue, 1 Jul 2025 17:05:10 +0300
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
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 v3 00/10] gpio: sysfs: add a per-chip export/unexport
 attribute pair

On Mon, Jun 30, 2025 at 02:37:07PM +0200, Bartosz Golaszewski 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.
> 
> The series contains the 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 as well as a way to 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].

It seems I never expressed my overall opinion about this. I think the poking
sysfs and making it working with a new schema won't solve the issues that
character device was developed to target. If so, doing this just brings yet
another broken interface. I would be happy to be mistaken!

If I am mistaken, I would like to see a summary here that explains that clearly
that the new sysfs approach does not inherit design flaws of the original
implementation.

> [1] https://lore.kernel.org/all/CAMRc=McUCeZcU6co1aN54rTudo+JfPjjForu4iKQ5npwXk6GXA@mail.gmail.com/
> [2] https://github.com/brgl/gpio-sysfs-compat-tests

-- 
With Best Regards,
Andy Shevchenko