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

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Date:   Tue, 28 Nov 2023 17:40:13 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kent Gibson <warthog618@...il.com>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 2/2] gpio: use a mutex to protect the list of GPIO devices

On Tue, Nov 28, 2023 at 5:09 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Mon, Nov 27, 2023 at 08:37:16PM +0100, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > 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.
>
> ...
>
> > +     scoped_guard(mutex, &gpio_devices_lock) {
>
> This is a lot of churn with this because of switching to RAII.
> Can the body be firstly moved to a helper?
>

But that would mean more churn. I don't get why you insist on
splitting these everytime. We're going from spinlock to a mutex so we
may as well use guards right away.

> > +             /*
> > +              * TODO: this allocates a Linux GPIO number base in the global
> > +              * GPIO numberspace for this chip. In the long run we want to
> > +              * get *rid* of this numberspace and use only descriptors, but
> > +              * it may be a pipe dream. It will not happen before we get rid
> > +              * of the sysfs interface anyways.
> > +              */
>
> ...
>
> >       list_for_each_entry(gdev, &gpio_devices, list)
> > +             if (index-- == 0)
> >                       return gdev;
>
> I believe this is better with outer {}.
>

Right.

Bart

> --
> With Best Regards,
> Andy Shevchenko
>
>