linux-kernel - [PATCH 2/2] ASoC: wm8996: ensure lower bounds of 1 for timeout

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Date:	Sun,  8 Mar 2015 06:02:38 -0400
From:	Nicholas Mc Guire <hofrat@...dl.org>
To:	Liam Girdwood <lgirdwood@...il.com>
Cc:	Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Xiubo Li <Li.Xiubo@...escale.com>,
	Sachin Kamat <sachin.kamat@...sung.com>,
	Axel Lin <axel.lin@...ics.com>,
	abdoulaye berthe <berthe.ab@...il.com>,
	patches@...nsource.wolfsonmicro.com, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org, Nicholas Mc Guire <hofrat@...dl.org>
Subject: [PATCH 2/2] ASoC: wm8996: ensure lower bounds of 1 for timeout

wait_for_completion_timeout can be called with timeout == 0 due to
msecs_to_jiffies(2) == 1 for HZ < 1000 and usecs_to_jiffies(300) == 1
for all reasonable values of HZ, thus the following timeout /= 2; sets
timeout to 0. This patch simply adds a lower-bounds of 1.

Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
---

line numbers from wm9666.c linux-next -next-20150306

2101      /* Wait for the FLL to lock, using the interrupt if possible */
2102      if (Fref > 1000000)
2103              timeout = usecs_to_jiffies(300);
2104      else
2105              timeout = msecs_to_jiffies(2);
2106 
2107      /* Allow substantially longer if we've actually got the IRQ, poll
2108       * at a slightly higher rate if we don't.
2109       */
2110      if (i2c->irq)
2111              timeout *= 10;
2112      else
2113              timeout /= 2;
2114
2115      ret = wait_for_completion_timeout(&wm8996->fll_lock,
2116                                        timeout);

The call-path here would then be: 
 wait_for_completion_timeout(...,timeout)
  -> wait_for_common action==schedule_timeout
   -> schedule_timeout(timeout)
      ...
      expire = timeout + jiffies;

so expire == jiffies here and the timer would expire immediately
for systems with HZ<1000 due to msecs_to_jiffies(2) == 1 and the
following timeout /= 2 -> timeout == 0, which is probably a bit 
more that a "slightly higher rate".

This was only compile tested for exynos_defconfig + CONFIG_COMPILE_TEST=y,
SND_SOC_ALL_CODECS=m (implies CONFIG_SND_SOC_WM8996=m)

Patch is against 4.0-rc2 linux-next (localversion-next is -next-20150306)

 sound/soc/codecs/wm8996.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sound/soc/codecs/wm8996.c b/sound/soc/codecs/wm8996.c
index 24d9705..5ded102 100644
--- a/sound/soc/codecs/wm8996.c
+++ b/sound/soc/codecs/wm8996.c
@@ -2110,7 +2110,8 @@ static int wm8996_set_fll(struct snd_soc_codec *codec, int fll_id, int source,
 	if (i2c->irq)
 		timeout *= 10;
 	else
-		timeout /= 2;
+		/* ensure timeout of atleast 1 jiffies */
+		timeout = timeout/2 ? : 1;
 
 	for (retry = 0; retry < 10; retry++) {
 		time_left = wait_for_completion_timeout(&wm8996->fll_lock,
-- 
1.7.10.4

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