clockevents: Stop unused clockevent devices

To avoid getting spurious interrupts on a tickless CPU, clockevent
device can now be stopped by switching to ONESHOT_STOPPED state.

The natural place for handling this transition is tick_program_event().

On 'expires == KTIME_MAX', we skip programming the event and so we need
to fix such call sites as well, to always call tick_program_event()
irrespective of the expires value.

Once the clockevent device is required again, check if it was earlier
put into ONESHOT_STOPPED state. If yes, switch its state to ONESHOT
before programming its event.

To make sure we haven't missed any corner case, add a WARN() for the
case where we try to reprogram clockevent device while we aren't
configured in ONESHOT_STOPPED state.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: linaro-kernel@lists.linaro.org
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5146b07be7f0bc497e0ebae036590ec2fa73e540.1428031396.git.viresh.kumar@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 16 insertions, 0 deletions

diff --git a/kernel/time/tick-oneshot.c b/kernel/time/tick-oneshot.c
index 67a64b1670bf..f8de75715c2f 100644
--- a/kernel/time/tick-oneshot.c
+++ b/kernel/time/tick-oneshot.c
@@ -28,6 +28,22 @@ int tick_program_event(ktime_t expires, int force)
 {
 	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
 
+	if (unlikely(expires.tv64 == KTIME_MAX)) {
+		/*
+		 * We don't need the clock event device any more, stop it.
+		 */
+		clockevents_set_state(dev, CLOCK_EVT_STATE_ONESHOT_STOPPED);
+		return 0;
+	}
+
+	if (unlikely(dev->state == CLOCK_EVT_STATE_ONESHOT_STOPPED)) {
+		/*
+		 * We need the clock event again, configure it in ONESHOT mode
+		 * before using it.
+		 */
+		clockevents_set_state(dev, CLOCK_EVT_STATE_ONESHOT);
+	}
+
 	return clockevents_program_event(dev, expires, force);
 }