linux-kernel - Re: [PATCH] leds: Fix locking for WM8350

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Message-ID: <20081118083346.GB1494@ucw.cz>
Date:	Tue, 18 Nov 2008 09:33:47 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Richard Purdie <rpurdie@...ys.net>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] leds: Fix locking for WM8350

On Mon 2008-11-17 15:33:15, Richard Purdie wrote:
> On Sat, 2008-11-15 at 19:14 +0000, Mark Brown wrote:
> > On Sat, Nov 15, 2008 at 07:51:20PM +0100, Pavel Machek wrote:
> > > On Sat 2008-11-15 17:50:50, Mark Brown wrote:
> > 
> > > > Yes, that'd be safer though I'd be surprised to see systems that could
> > > > trigger it.
> > 
> > > Yes, they are uncommon. They exist; SPARC, IIRC. Plus you need
> > 
> > Exceptionally uncommon with the systems the WM8350 gets used with -
> > it's a primary PMIC for mobile devices so anything other than
> > uniprocessor ARM would be surprising.
> > 
> > > barriers on anything SMP... Just use atomic_t.
> > 
> > I was intending to do so next time I spin the patch.  Andrew had some
> > other comments and I don't have any test systems when I'm not in the
> > office anyway.
> 
> I've not looked in detail at the code but it looks like a maximum of a
> 32 bit value where you don't actually care which write succeeds as long
> as it takes one of the values written? I don't see why that particular
> variable needs any locking or to be atomic?

Yes.. but it would hurt if you  find 42 there, right? So atomic_t is
safer. gcc is alowed to do fancy optimalizations on plain integers....

-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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