[ 26/76] ARM: OMAP: counter: add locking to read_persistent_clock

Greg Kroah-Hartman
2012-10-19T03:03:44Z

From: Colin Cross <ccross@android.com>

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@android.com>
Signed-off-by: R Sricharan <r.sricharan@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm/plat-omap/counter_32k.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)

--- a/arch/arm/plat-omap/counter_32k.c
+++ b/arch/arm/plat-omap/counter_32k.c
@@ -55,22 +55,29 @@ static u32 notrace omap_32k_read_sched_c
* 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);
}

/**