linux-kernel - Re: [PATCH 1/8] gpiolib: check the return value of gpio_chip::get

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Message-ID: <CAMRc=MduJK0_gat2aVQbR9udYNj9oDcoN=me0wa4K6L8dX_52Q@mail.gmail.com>
Date: Wed, 19 Feb 2025 09:50:55 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, stable@...r.kernel.org
Subject: Re: [PATCH 1/8] gpiolib: check the return value of gpio_chip::get_direction()

On Wed, Feb 19, 2025 at 9:38 AM Marek Szyprowski
<m.szyprowski@...sung.com> wrote:
>
> Hi Bartosz,
>
> On 10.02.2025 11:51, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > As per the API contract - gpio_chip::get_direction() may fail and return
> > a negative error number. However, we treat it as if it always returned 0
> > or 1. Check the return value of the callback and propagate the error
> > number up the stack.
> >
>
> This change breaks bcm2835 pincontrol/gpio driver (and probably others)
> in next-20250218. The problem is that some gpio lines are initially
> configured as alternate function (i.e. uart) and .get_direction returns
> -EINVAL for them, what in turn causes the whole gpio chip fail to
> register. Here is the log with WARN_ON() added to line
> drivers/pinctrl/bcm/pinctrl-bcm2835.c:350 from Raspberry Pi 4B:
>
> Any suggestions how to fix this issue? Should we add
> GPIO_LINE_DIRECTION_UNKNOWN?
>

That would be quite an intrusive change and not something for the
middle of the release cycle. I think we need to revert to the previous
behavior for this particular use-case: check ret for EINVAL and assume
it means input as it's the "safe" setting. Now the question is - can
this only happen during the chip registration or should we filter out
EINVAL at each gpiod_get_direction() call?

Bart