[PATCH v3] tick/broadcast: Allow later registered device enter oneshot mode

[Jindong Yue]

Broadcast device is switched to oneshot mode in
tick_switch_to_oneshot() -> tick_broadcast_switch_to_oneshot().

If build broadcast clock event device driver as module, and
install it after system enters oneshot mode, then it will
stay in periodic mode forever.

This patch allows such broadcast device switch to oneshot
mode when register.

Signed-off-by: Jindong Yue <jindong.yue@xxxxxxx>
---

v3 changes: 
- Remove useless declaration: tick_handle_oneshot_broadcast()
- Refine some comments

v2 changes:
- Remove below condition check before switch new installed
  broadcast device to oneshot mode:
  dev->event_handler != tick_handle_oneshot_broadcast
- Put tick_clock_notify() after check system not runs in
  oneshot mode

---
 kernel/time/tick-broadcast.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 36d7464c8962..f4bc384d8f1b 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -107,6 +107,19 @@ void tick_install_broadcast_device(struct clock_event_device *dev)
 	tick_broadcast_device.evtdev = dev;
 	if (!cpumask_empty(tick_broadcast_mask))
 		tick_broadcast_start_periodic(dev);
+
+	if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT))
+		return;
+
+	/*
+	 * If the system already runs in oneshot mode, switch the newly
+	 * registered broadcast device to oneshot mode explicitly.
+	 */
+	if (tick_broadcast_oneshot_active()) {
+		tick_broadcast_switch_to_oneshot();
+		return;
+	}
+
 	/*
 	 * Inform all cpus about this. We might be in a situation
 	 * where we did not switch to oneshot mode because the per cpu
@@ -115,8 +128,7 @@ void tick_install_broadcast_device(struct clock_event_device *dev)
 	 * notification the systems stays stuck in periodic mode
 	 * forever.
 	 */
-	if (dev->features & CLOCK_EVT_FEAT_ONESHOT)
-		tick_clock_notify();
+	tick_clock_notify();
 }
 
 /*
-- 
2.17.1