linux-kernel - Re: [PATCH v2 4/5] gpiolib: cdev: reduce locking in gpio_desc_to

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Message-ID: <ZXse4UDKGlVqzsyD@smile.fi.intel.com>
Date:   Thu, 14 Dec 2023 17:27:29 +0200
From:   Andy Shevchenko <andy@...nel.org>
To:     Kent Gibson <warthog618@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        brgl@...ev.pl, linus.walleij@...aro.org
Subject: Re: [PATCH v2 4/5] gpiolib: cdev: reduce locking in
 gpio_desc_to_lineinfo()

On Thu, Dec 14, 2023 at 11:19:01PM +0800, Kent Gibson wrote:
> On Thu, Dec 14, 2023 at 05:10:23PM +0200, Andy Shevchenko wrote:
> > On Thu, Dec 14, 2023 at 05:58:13PM +0800, Kent Gibson wrote:
> > > Reduce the time holding the gpio_lock by snapshotting the desc flags,
> > > rather than testing them individually while holding the lock.
> > >
> > > Accept that the calculation of the used field is inherently racy, and
> > > only check the availability of the line from pinctrl if other checks
> > > pass, so avoiding the check for lines that are otherwise in use.

...

> > > -	spin_lock_irqsave(&gpio_lock, flags);
> >
> > Shouldn't this be covered by patch 1 (I mean conversion to scoped_guard()
> > instead of spinlock)?
> >
> 
> Read the cover letter.
> Doing that made the change larger, as flags gets removed then restored.
> I had also thought the flag tests would get indented then unindented, but
> if we use guard() the indentation should remain unchanged.

I'm fine with that as I pointed out (have you received that mail? I had
problems with my mail server) the dflags is better semantically, so restoration
with _different_ name is fine.

> Can do it in 1 if you are happy with the flags declaration being
> removed in patch 1 and restored in 4.

Definitely.

-- 
With Best Regards,
Andy Shevchenko