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>

1 files changed, 31 insertions, 0 deletions

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 0d96cde9ee5d..5a40d14daa9f 100644
--- 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;
@@ -275,6 +279,33 @@ static inline cycle_t clocksource_read(struct clocksource *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
  * @cycles:     Cycles