linux-kernel - Re: [PATCH 3/4] gpiolib: cdev: reduce locking in gpio_desc_to

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Message-ID: <ZXnJply1tPnTN_-O@rigel>
Date:   Wed, 13 Dec 2023 23:11:34 +0800
From:   Kent Gibson <warthog618@...il.com>
To:     Andy Shevchenko <andy@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        brgl@...ev.pl, linus.walleij@...aro.org
Subject: Re: [PATCH 3/4] gpiolib: cdev: reduce locking in
 gpio_desc_to_lineinfo()

On Wed, Dec 13, 2023 at 10:07:28PM +0800, Kent Gibson wrote:
> On Wed, Dec 13, 2023 at 03:56:27PM +0200, Andy Shevchenko wrote:
> > On Tue, Dec 12, 2023 at 01:42:52PM +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 availabilty of the line from pinctrl if other checks
> > > pass, so avoiding the check for lines that are otherwise in use.
> >
> > ...
> >
> > > -	bool ok_for_pinctrl;
> > > -	unsigned long flags;
> > > +	unsigned long iflags, dflags;
> >
> > With a preliminary conversion to cleanup.h this whole change becomes cleaner,
> > no?
> >
>
> You mean the scoped guards?  Dunno - haven't used them.
> Care to provide more detail?
>

Ok, so changing the spin_lock/unlock to

       scoped_guard(spinlock_irqsave, &gpio_lock) {
       ...
       }

you no longer need the iflags at all, and can rename dflags to flags.
Got it.

Cheers,
Kent.