linux-kernel - V4L2 drivers: potentially dangerous and inefficient msecs_to

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Date:	Mon, 14 Sep 2009 23:07:41 +0200
From:	Andreas Mohr <andi@...as.de>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Mauro Carvalho Chehab <mchehab@...radead.org>
Cc:	Luca Risolia <luca.risolia@...dio.unibo.it>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: V4L2 drivers: potentially dangerous and inefficient
	msecs_to_jiffies() calculation

Hi all,

./drivers/media/video/sn9c102/sn9c102_core.c
,
./drivers/media/video/et61x251/et61x251_core.c
and
./drivers/media/video/zc0301/zc0301_core.c
do
                            cam->module_param.frame_timeout *
                            1000 * msecs_to_jiffies(1) );
multiple times each.
What they should do instead is
frame_timeout * msecs_to_jiffies(1000), I'd think.
msecs_to_jiffies(1) is quite a bit too boldly assuming
that all of the msecs_to_jiffies(x) implementation branches
always round up.

Not to mention that the current implementation needs one additional
multiplication operation as opposed to constant-aggregating it into the
msecs_to_jiffies() argument and thus nicely evaporating it into nirvana.

HTH,

Andreas Mohr
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