Re: [PATCH 2/2] gpio: use a mutex to protect the list of GPIO devices

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Nov 27, 2023 at 8:37 PM Bartosz Golaszewski <brgl@xxxxxxxx> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
>
> The global list of GPIO devices is never modified or accessed from
> atomic context so it's fine to protect it using a mutex. Add a new
> global lock dedicated to the gpio_devices list and use it whenever
> accessing or modifying it.
>
> While at it: fold the sysfs registering of existing devices into
> gpiolib.c and make gpio_devices static within its compilation unit.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

Nice! I might have found some snag:

gpio_device_find() still does guard(spinlock_irqsave)(&gpio_lock);
shouldn't that be switched to the mutex?

On top of this I can update my patch to the delete the comment
for gpio_lock to just rename that thing to gpio_descriptor_lock
and document it as such.

But when I think about it: gpio[_decriptor]_lock can now (after this
patch) be moved into struct gpio_chip as it is really just protecting
the descriptors on the same chip from simultaneous modification,
especially desc->flags. This is a BIG WIN because it makes it a local
lock not a global one, do you wanna try it or should I? (On top of
these two patches, then.)

Yours,
Linus Walleij