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>

3 files changed, 22 insertions, 4 deletions

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index dc6afb485027..4922f1b805ea 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -331,6 +331,10 @@ int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
         if (dev->state == CLOCK_EVT_STATE_SHUTDOWN)
                 return 0;
 
+        /* We must be in ONESHOT state here */
+        WARN_ONCE(dev->state != CLOCK_EVT_STATE_ONESHOT, "Current state: %d\n",
+                  dev->state);
+
         /* Shortcut for clockevent devices that can deal with ktime. */
         if (dev->features & CLOCK_EVT_FEAT_KTIME)
                 return dev->set_next_ktime(expires, dev);
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 4adf32067862..278d4b36fd94 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -550,8 +550,7 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
         if (cpu_base->hang_detected)
                 return;
 
-        if (cpu_base->expires_next.tv64 != KTIME_MAX)
-                tick_program_event(cpu_base->expires_next, 1);
+        tick_program_event(cpu_base->expires_next, 1);
 }
 
 /*
@@ -1237,8 +1236,7 @@ retry:
         raw_spin_unlock(&cpu_base->lock);
 
         /* Reprogramming necessary ? */
-        if (expires_next.tv64 == KTIME_MAX ||
-            !tick_program_event(expires_next, 0)) {
+        if (!tick_program_event(expires_next, 0)) {
                 cpu_base->hang_detected = 0;
                 return;
         }
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);
 }