Re: [PATCH V2] gpu: host1x: handle the correct # of syncpt regs

From: Thierry Reding <thierry.reding@gmail.com>
To: Stephen Warren <swarren@wwwdotorg.org>
Cc: linux-tegra@vger.kernel.org,
	"Stephen Warren" <swarren@nvidia.com>,
	"Terje Bergström" <tbergstrom@nvidia.com>,
	dri-devel@lists.freedesktop.org
Subject: Re: [PATCH V2] gpu: host1x: handle the correct # of syncpt regs
Date: Tue, 22 Apr 2014 09:15:27 +0200	[thread overview]
Message-ID: <20140422071526.GA11766@ulmo> (raw)
In-Reply-To: <534C4ADF.7010607@wwwdotorg.org>

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On Mon, Apr 14, 2014 at 02:53:51PM -0600, Stephen Warren wrote:
> On 04/04/2014 04:31 PM, Stephen Warren wrote:
> > From: Stephen Warren <swarren@nvidia.com>
> > 
> > BIT_WORD() truncates rather than rounds, so the loops in
> > syncpt_thresh_isr() and _host1x_intr_disable_all_syncpt_intrs() use <=
> > rather than < in an attempt to process the correct number of registers
> > when rounding of the conversion of count of bits to count of words is
> > necessary. However, when rounding isn't necessary because the value is
> > already a multiple of the divisor (as is the case for all values of
> > nb_pts the code actually sees), this causes one too many registers to
> > be processed.
> > 
> > Solve this by using and explicit DIV_ROUND_UP() call, rather than
> > BIT_WORD(), and comparing with < rather than <=.
> 
> I don't see this in linux-next yet.

Just in case you haven't noticed, this this was merged in v3.15-rc2.
I've also Cc'ed stable so that it can be applied as far back as 3.10
when the code it fixes was introduced.

Thierry

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