Re: [PATCH] gpio: Revert regression in sysfs-gpio (gpiolib.c)

From: Linus Walleij <linus.walleij@linaro.org>
To: Marcelo Roberto Jimenez <marcelo.jimenez@gmail.com>
Cc: stable <stable@vger.kernel.org>,
	regressions@lists.linux.dev,  Bartosz Golaszewski <brgl@bgdev.pl>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	 Thierry Reding <treding@nvidia.com>,
	Vidya Sagar <vidyas@nvidia.com>,
	 Geert Uytterhoeven <geert@linux-m68k.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	 Edmond Chung <edmondchung@google.com>,
	Andrew Chant <achant@google.com>,
	 Will McVicker <willmcvicker@google.com>,
	Sergio Tanzilli <tanzilli@acmesystems.it>
Subject: Re: [PATCH] gpio: Revert regression in sysfs-gpio (gpiolib.c)
Date: Sat, 12 Feb 2022 17:54:48 +0100	[thread overview]
Message-ID: <CACRpkda=0=Hcyyote+AfwoLKPGak7RV6VFt6b0fMVWBe8veTwA@mail.gmail.com> (raw)
In-Reply-To: <CACjc_5q247Yb8t8PfJcudVAPFYQcioREAE3zj8OtPR-Ug_x=tA@mail.gmail.com>

On Fri, Feb 11, 2022 at 11:36 PM Marcelo Roberto Jimenez
<marcelo.jimenez@gmail.com> wrote:

> > Which devicetree or boardfile in the upstream Linux kernel is this system
> > using?
>
> arch/arm/boot/dts/at91-ariettag25.dts

So this system was added in 2015 which is the same year that
we marked the GPIO sysfs ABI obsolete:

commit fe95046e960b4b76e73dc1486955d93f47276134
Author: Linus Walleij <linus.walleij@linaro.org>
Date:   Thu Oct 22 09:58:34 2015 +0200

    gpio: ABI: mark the sysfs ABI as obsolete

Why is this system which was clearly developed while we deprecated
the sysfs ABI so dependent on it?

I am curious about the usecases and how deeply you have built
yourselves into this.

> In any case, the upstream file should be enough to test the issue reported here.

The thing is that upstream isn't super happy that you have been
making yourselves dependent on features that we are actively
discouraging and then demanding that we support these features.

Anyway, what is wrong with using the GPIO character device and libgpiod
on this system? What kind of userspace are you creating that
absolutely requires that you use sysfs?

I hope not one of these?
https://docs.kernel.org/driver-api/gpio/drivers-on-gpio.html

Here is some info about what we have been doing with the GPIO
character device:

https://docs.kernel.org/driver-api/gpio/using-gpio.html
https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/tree/

Here is Bartosz presenting it:
https://www.youtube.com/watch?v=BK6gOLVRKuU

Since I patched the kernel such that you cannot activate the sysfs
ABI without also activating the character device I *know* that you
have it on your system.

Yours,
Linus Walleij