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 0d96cde..5a40d14 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -144,6 +144,8 @@
* 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 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;
@@ -275,6 +279,33 @@
}
/**
+ * 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
* @cycles: Cycles
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 900f1b6..687dff4 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -182,7 +182,7 @@
*/
static void change_clocksource(void)
{
- struct clocksource *new;
+ struct clocksource *new, *old;
new = clocksource_get_next();
@@ -191,11 +191,16 @@
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 @@
ntp_init();
clock = clocksource_get_next();
+ clocksource_enable(clock);
clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
clock->cycle_last = clocksource_read(clock);