linux-kernel - [PATCH] clocksource: save mult_orig in clocksource

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Date:	Fri, 19 Jun 2009 00:24:32 +0900
From:	Magnus Damm <magnus.damm@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	johnstul@...ibm.com, mingo@...e.hu, lethal@...ux-sh.org,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	Magnus Damm <magnus.damm@...il.com>
Subject: [PATCH] clocksource: save mult_orig in clocksource_disable()

From: Magnus Damm <damm@...l.co.jp>

Save clocksource mult_orig in clocksource_disable().

To fix the common case where ->enable() does not setup
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@...l.co.jp>
---

 include/linux/clocksource.h |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- 0001/include/linux/clocksource.h
+++ work/include/linux/clocksource.h	2009-06-19 00:12:16.000000000 +0900
@@ -293,7 +293,11 @@ static inline int clocksource_enable(str
 	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 +313,12 @@ static inline int clocksource_enable(str
  */
 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);
 }
--
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