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

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Message-ID: <20250702101212.GA47772@rigel>
Date: Wed, 2 Jul 2025 18:12:12 +0800
From: Kent Gibson <warthog618@...il.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Andy Shevchenko <andriy.shevchenko@...el.com>,
	Ahmad Fatoum <a.fatoum@...gutronix.de>,
	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 Wed, Jul 02, 2025 at 11:45:02AM +0200, Bartosz Golaszewski wrote:
> On Wed, Jul 2, 2025 at 5:54 AM Kent Gibson <warthog618@...il.com> wrote:
> >
> > On Tue, Jul 01, 2025 at 05:05:10PM +0300, Andy Shevchenko wrote:
> > >
> > > 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.
> > >
>
> You cut out the link to the discussion that preceded this series where
> a good summary is in the very first email. Anyway: the gist is: people
> need to do some basic GPIO fiddling early on from initramfs that may
> not have any tools other than basic shell utils from busybox. This
> series is not about improving or extending the sysfs interface - it's
> about removing its reliance on global GPIO numbers. And that's about
> it. We don't add any new features really, just move the GPIO line
> groups into their respective chip directories and make exporting use
> the hardware offsets, not global numbers.
>

And that is the problem I have with it - it is just removing the global
numbering, while keeping all the other sysfs baggage.
Instead I think it should be thought of as adding a new minimal sysfs
alternative to cdev, based on the old sysfs.

> >
> > Indeed.  I've already expressed my reservations about supporting the whole
> > of the existing sysfs capabilties, but I've otherwise tried to remain out
> > of the discussion.
> >
> > To reiterate my position:
> > While I am all for maintaining sysfs in some form to cater for those
> > rare cases where cdev is too heavyweight, IMHO it is a mistake to
> > support the existing sysfs capabilities in toto.  Take the opportunity to
> > remove the parts of the sysfs interface that don't work well.
>
> Doesn't the last patch do it? We cannot remove it without giving
> user-space some time to switch. This series does everything in a
> backward compatible way and then isolates the old bits under ifdefs so
> that when the time comes it's just a matter of removing everything
> guarded by them.
>

Not suggesting any changes to the existing sysfs here, only your new.

> > The new sysfs should only provide the features required by those rare use
> > cases, which IIUC would be basic sets and gets, and exclude those features
> > not required, particularly warts like edges.
> >
> > If you need more advanced features then use cdev.
> > If all you need is basic sets and gets then sysfs is probably fine.
> >
> > If that isn't the case then there should be some explanation as to why those
> > sysfs features are being maintained.  Treat this as a new interface.
> >
>
> 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.

Cheers,
Kent.