[ 3.5.yuz extended stable ] Patch "ARM: OMAP: counter: add locking to read_persistent_clock" has been added to staging queue

Herton Ronaldo Krzesinski herton.krzesinski at canonical.com
Thu Nov 15 05:49:22 UTC 2012

This is a note to let you know that I have just added a patch titled

    ARM: OMAP: counter: add locking to read_persistent_clock

to the linux-3.5.y-queue branch of the 3.5.yuz extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.yuz tree, see



>From 83efd23938f8cf62a56d85ef51ff54ba815fa758 Mon Sep 17 00:00:00 2001
From: Colin Cross <ccross at android.com>
Date: Mon, 8 Oct 2012 14:01:12 -0700
Subject: [PATCH] ARM: OMAP: counter: add locking to read_persistent_clock

commit 9d7d6e363b06934221b81a859d509844c97380df upstream.

read_persistent_clock uses a global variable, use a spinlock to
ensure non-atomic updates to the variable don't overlap and cause
time to move backwards.

Signed-off-by: Colin Cross <ccross at android.com>
Signed-off-by: R Sricharan <r.sricharan at ti.com>
Signed-off-by: Tony Lindgren <tony at atomide.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
 arch/arm/plat-omap/counter_32k.c |   21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/arch/arm/plat-omap/counter_32k.c b/arch/arm/plat-omap/counter_32k.c
index 2132c4f..721eae5 100644
--- a/arch/arm/plat-omap/counter_32k.c
+++ b/arch/arm/plat-omap/counter_32k.c
@@ -52,22 +52,29 @@ static u32 notrace omap_32k_read_sched_clock(void)
  * nsecs and adds to a monotonically increasing timespec.
 static struct timespec persistent_ts;
-static cycles_t cycles, last_cycles;
+static cycles_t cycles;
 static unsigned int persistent_mult, persistent_shift;
+static DEFINE_SPINLOCK(read_persistent_clock_lock);
 static void omap_read_persistent_clock(struct timespec *ts)
 	unsigned long long nsecs;
-	cycles_t delta;
-	struct timespec *tsp = &persistent_ts;
+	cycles_t last_cycles;
+	unsigned long flags;
+	spin_lock_irqsave(&read_persistent_clock_lock, flags);

 	last_cycles = cycles;
 	cycles = sync32k_cnt_reg ? __raw_readl(sync32k_cnt_reg) : 0;
-	delta = cycles - last_cycles;

-	nsecs = clocksource_cyc2ns(delta, persistent_mult, persistent_shift);
+	nsecs = clocksource_cyc2ns(cycles - last_cycles,
+					persistent_mult, persistent_shift);
+	timespec_add_ns(&persistent_ts, nsecs);
+	*ts = persistent_ts;

-	timespec_add_ns(tsp, nsecs);
-	*ts = *tsp;
+	spin_unlock_irqrestore(&read_persistent_clock_lock, flags);


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