linux-kernel - Re: [PATCH] gpiolib: don't allow setting values on input lines

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Message-ID: <CAMRc=MdsRWNVT0XC1DvwBdhZFsVZO6DeMrVePKgiF4Mj_Ryykg@mail.gmail.com>
Date: Wed, 9 Apr 2025 18:43:47 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, Kent Gibson <warthog618@...il.com>, 
	Matti Vaittinen <mazziesaccount@...il.com>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] gpiolib: don't allow setting values on input lines

On Wed, Apr 9, 2025 at 4:38 PM Andy Shevchenko
<andriy.shevchenko@...el.com> wrote:
>
> On Fri, Mar 14, 2025 at 11:35:21AM +0100, Bartosz Golaszewski wrote:
> > On Fri, Mar 14, 2025 at 11:33 AM Linus Walleij <linus.walleij@...aro.org> wrote:
> > > On Tue, Mar 11, 2025 at 3:20 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> > >
> > > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > > >
> > > > Some drivers as well as the character device and sysfs code check
> > > > whether the line actually is in output mode before allowing the user to
> > > > set a value.
> > > >
> > > > However, GPIO value setters now return integer values and can indicate
> > > > failures. This allows us to move these checks into the core code.
> > > >
> > > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > Makes sense, if there are regressions let's smoke them out
> > > in linux-next.
> > >
> > > Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> >
> > Thanks. I decided not to queue it for v6.15 for exactly that reason,
> > I'll pick it up early into the v6.16 cycle and let it sit in next for
> > several weeks.
>
> As far as I can tell from the reading of the code, this will break the open
> drain emulation. Am I mistaken?
>

Could you produce a call trace where this could result in a breakage?
I tested open-drain and open-source emulation but maybe I'm missing
something.

Bartosz