clocksource: add suspend callback

Add a clocksource suspend callback.  This callback can be used by the
clocksource driver to shutdown and perform any kind of late suspend
activities even though the clocksource driver itself is a non-sysdev
driver.

One example where this is useful is to fix the sh_cmt.c platform driver
that today suspends using the platform bus and shuts down the clocksource
too early.

With this callback in place the sh_cmt driver will suspend using the
clocksource and clockevent hooks and leave the platform device pm
callbacks unused.
Signed-off-by: NMagnus Damm <damm@opensource.se>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

include/linux/clocksource.h

@@ -154,6 +154,7 @@ extern u64 timecounter_cyc2time(struct timecounter *tc,
  * @max_idle_ns:	max idle time permitted by the clocksource (nsecs)
  * @flags:		flags describing special properties
  * @vread:		vsyscall based read
+ * @suspend:		suspend function for the clocksource, if necessary
  * @resume:		resume function for the clocksource, if necessary
  */
 struct clocksource {
@@ -172,6 +173,7 @@ struct clocksource {
 	u64 max_idle_ns;
 	unsigned long flags;
 	cycle_t (*vread)(void);
+	void (*suspend)(struct clocksource *cs);
 	void (*resume)(struct clocksource *cs);
 #ifdef CONFIG_IA64
 	void *fsys_mmio;        /* used by fsyscall asm code */
@@ -277,6 +279,7 @@ extern void clocksource_unregister(struct clocksource*);
 extern void clocksource_touch_watchdog(void);
 extern struct clocksource* clocksource_get_next(void);
 extern void clocksource_change_rating(struct clocksource *cs, int rating);
+extern void clocksource_suspend(void);
 extern void clocksource_resume(void);
 extern struct clocksource * __init __weak clocksource_default_clock(void);
 extern void clocksource_mark_unstable(struct clocksource *cs);

kernel/time/clocksource.c

@@ -440,6 +440,18 @@ static inline int clocksource_watchdog_kthread(void *data) { return 0; }
 
 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
 
+/**
+ * clocksource_suspend - suspend the clocksource(s)
+ */
+void clocksource_suspend(void)
+{
+	struct clocksource *cs;
+
+	list_for_each_entry_reverse(cs, &clocksource_list, list)
+		if (cs->suspend)
+			cs->suspend(cs);
+}
+
 /**
  * clocksource_resume - resume the clocksource(s)
  */

kernel/time/timekeeping.c

@@ -622,6 +622,7 @@ static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
 	write_sequnlock_irqrestore(&xtime_lock, flags);
 
 	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
+	clocksource_suspend();
 
 	return 0;
 }