clocksource: add enable() and disable() callbacks

Add enable() and disable() callbacks for clocksources.

This allows us to put unused clocksources in power save mode.  The
functions clocksource_enable() and clocksource_disable() wrap the
callbacks and are inserted in the timekeeping code to enable before use
and disable after switching to a new clocksource.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 0d96cde9ee5d90cc627ad901e7ab84870ee11de5..5a40d14daa9fab04bf641c1a11d82a1610ff7753 100644 (file)
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -144,6 +144,8 @@ extern u64 timecounter_cyc2time(struct timecounter *tc,
  *                             The ideal clocksource. A must-use where
  *                             available.
  * @read:              returns a cycle value, passes clocksource as argument
+ * @enable:            optional function to enable the clocksource
+ * @disable:           optional function to disable the clocksource
  * @mask:              bitmask for two's complement
  *                     subtraction of non 64 bit counters
  * @mult:              cycle to nanosecond multiplier (adjusted by NTP)
@@ -163,6 +165,8 @@ struct clocksource {
        struct list_head list;
        int rating;
        cycle_t (*read)(struct clocksource *cs);
+       int (*enable)(struct clocksource *cs);
+       void (*disable)(struct clocksource *cs);
        cycle_t mask;
        u32 mult;
        u32 mult_orig;
@@ -274,6 +278,33 @@ static inline cycle_t clocksource_read(struct clocksource *cs)
        return cs->read(cs);
 }
 
+/**
+ * clocksource_enable: - enable clocksource
+ * @cs:                pointer to clocksource
+ *
+ * Enables the specified clocksource. The clocksource callback
+ * function should start up the hardware and setup mult and field
+ * members of struct clocksource to reflect hardware capabilities.
+ */
+static inline int clocksource_enable(struct clocksource *cs)
+{
+       return cs->enable ? cs->enable(cs) : 0;
+}
+
+/**
+ * clocksource_disable: - disable clocksource
+ * @cs:                pointer to clocksource
+ *
+ * Disables the specified clocksource. The clocksource callback
+ * function should power down the now unused hardware block to
+ * save power.
+ */
+static inline void clocksource_disable(struct clocksource *cs)
+{
+       if (cs->disable)
+               cs->disable(cs);
+}
+
 /**
  * cyc2ns - converts clocksource cycles to nanoseconds
  * @cs:                Pointer to clocksource

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 900f1b6598d11ba52490f2aa52074a25a0daa206..687dff49f6e7da5ec92199f6bbae08de57e5ba43 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -182,7 +182,7 @@ EXPORT_SYMBOL(do_settimeofday);
  */
 static void change_clocksource(void)
 {
-       struct clocksource *new;
+       struct clocksource *new, *old;
 
        new = clocksource_get_next();
 
@@ -191,11 +191,16 @@ static void change_clocksource(void)
 
        clocksource_forward_now();
 
-       new->raw_time = clock->raw_time;
+       if (clocksource_enable(new))
+               return;
 
+       new->raw_time = clock->raw_time;
+       old = clock;
        clock = new;
+       clocksource_disable(old);
+
        clock->cycle_last = 0;
-       clock->cycle_last = clocksource_read(new);
+       clock->cycle_last = clocksource_read(clock);
        clock->error = 0;
        clock->xtime_nsec = 0;
        clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
@@ -292,6 +297,7 @@ void __init timekeeping_init(void)
        ntp_init();
 
        clock = clocksource_get_next();
+       clocksource_enable(clock);
        clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
        clock->cycle_last = clocksource_read(clock);