clocksource: Save mult_orig in clocksource_disable()

To fix the common case where ->enable() does not set up
mult, make sure mult_orig is saved in mult on disable.

Also add comments to explain why we do this.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Cc: johnstul@us.ibm.com
Cc: lethal@linux-sh.org
Cc: akpm@linux-foundation.org
LKML-Reference: <20090618152432.10136.9932.sendpatchset@rx1.opensource.se>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 13 insertions, 1 deletions

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index c56457c8334e..1219be4fb42e 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -293,7 +293,12 @@ static inline int clocksource_enable(struct clocksource *cs)
         if (cs->enable)
                 ret = cs->enable(cs);
 
-        /* save mult_orig on enable */
+        /*
+         * The frequency may have changed while the clocksource
+         * was disabled. If so the code in ->enable() must update
+         * the mult value to reflect the new frequency. Make sure
+         * mult_orig follows this change.
+         */
         cs->mult_orig = cs->mult;
 
         return ret;
@@ -309,6 +314,13 @@ static inline int clocksource_enable(struct clocksource *cs)
  */
 static inline void clocksource_disable(struct clocksource *cs)
 {
+        /*
+         * Save mult_orig in mult so clocksource_enable() can
+         * restore the value regardless if ->enable() updates
+         * the value of mult or not.
+         */
+        cs->mult = cs->mult_orig;
+
         if (cs->disable)
                 cs->disable(cs);
 }