linux-kernel - Re: [PATCH v5 0/5] gpiolib: cdev: relocate debounce_period

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Date: Tue, 19 Dec 2023 10:30:49 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Kent Gibson <warthog618@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org, 
	linus.walleij@...aro.org, andy@...nel.org
Subject: Re: [PATCH v5 0/5] gpiolib: cdev: relocate debounce_period_us

On Tue, Dec 19, 2023 at 1:42 AM Kent Gibson <warthog618@...il.com> wrote:
>
> This series contains minor improvements to gpiolib-cdev.
>
> The banner change is relocating the debounce_period_us from gpiolib's
> struct gpio_desc to cdev's struct line.  Patch 1 stores the field
> locally in cdev.  Patch 2 removes the now unused field from gpiolib.
>
> Patch 3 is somewhat related and removes a FIXME from
> gpio_desc_to_lineinfo().  The FIXME relates to a race condition in
> the calculation of the used flag, but I would assert that from
> the userspace perspective the read operation itself is inherently racy.
> The line being reported as unused in the info provides no guarantee -
> it just an indicator that requesting the line is likely to succeed -
> assuming the line is not otherwise requested in the meantime.
> Given the overall operation is racy, trying to stamp out an unlikely
> race within the operation is pointless. Accept it as a possibility
> that has negligible side-effects and reduce the number of locks held
> simultaneously and the duration that the gpio_lock is held.
>
> Patches 1 and 3 introduce usage of guard() and scoped_guard() to cdev.
> Patch 4 replaces any remaining discrete lock/unlock calls around
> critical sections with guard() or scoped_guard().
>
> Patch 5 is unrelated to debounce or info, but addresses Andy's
> recent lamentation that the linereq get/set values functions are
> confusing and under documented.
> Figured I may as well add that while I was in there.
>

I applied patches 1,2, 4 and 5. I have one more suggestion for patch 3
so I held it off.

Bart