timekeeping: Add suspend and resume of clock event devices

Some clock event devices, for example such that belong to PM domains,
need to be handled in a spcial way during the timekeeping suspend
and resume (which takes place in the system core, or "syscore",
stages of system power transitions) in analogy with clock sources.

Introduce .suspend() and .resume() callbacks for clock event devices
that will be executed by timekeeping_suspend/_resume(), respectively,
next the the clock sources' .suspend() and .resume() callbacks.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

include/linux/clockchips.h

@@ -97,6 +97,8 @@ struct clock_event_device {
 	void			(*broadcast)(const struct cpumask *mask);
 	void			(*set_mode)(enum clock_event_mode mode,
 					    struct clock_event_device *);
+	void			(*suspend)(struct clock_event_device *);
+	void			(*resume)(struct clock_event_device *);
 	unsigned long		min_delta_ticks;
 	unsigned long		max_delta_ticks;
 
@@ -156,6 +158,9 @@ clockevents_calc_mult_shift(struct clock_event_device *ce, u32 freq, u32 minsec)
 				      freq, minsec);
 }
 
+extern void clockevents_suspend(void);
+extern void clockevents_resume(void);
+
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
 extern void clockevents_notify(unsigned long reason, void *arg);
 #else
@@ -164,6 +169,9 @@ extern void clockevents_notify(unsigned long reason, void *arg);
 
 #else /* CONFIG_GENERIC_CLOCKEVENTS_BUILD */
 
+static inline void clockevents_suspend(void) {}
+static inline void clockevents_resume(void) {}
+
 #define clockevents_notify(reason, arg) do { } while (0)
 
 #endif

kernel/time/clockevents.c

@@ -397,6 +397,30 @@ void clockevents_exchange_device(struct clock_event_device *old,
 	local_irq_restore(flags);
 }
 
+/**
+ * clockevents_suspend - suspend clock devices
+ */
+void clockevents_suspend(void)
+{
+	struct clock_event_device *dev;
+
+	list_for_each_entry_reverse(dev, &clockevent_devices, list)
+		if (dev->suspend)
+			dev->suspend(dev);
+}
+
+/**
+ * clockevents_resume - resume clock devices
+ */
+void clockevents_resume(void)
+{
+	struct clock_event_device *dev;
+
+	list_for_each_entry(dev, &clockevent_devices, list)
+		if (dev->resume)
+			dev->resume(dev);
+}
+
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
 /**
  * clockevents_notify - notification about relevant events

kernel/time/timekeeping.c

@@ -773,6 +773,7 @@ static void timekeeping_resume(void)
 
 	read_persistent_clock(&ts);
 
+	clockevents_resume();
 	clocksource_resume();
 
 	write_seqlock_irqsave(&tk->lock, flags);
@@ -832,6 +833,7 @@ static int timekeeping_suspend(void)
 
 	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
 	clocksource_suspend();
+	clockevents_suspend();
 
 	return 0;
 }