linux-kernel - [PATCH] tick/broadcast: Allow later probed device enter oneshot mode

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Date:   Mon, 29 Mar 2021 13:25:55 +0800
From:   Jindong Yue <jindong.yue@....com>
To:     fweisbec@...il.com, tglx@...utronix.de, mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, jindong.yue@....com
Subject: [PATCH] tick/broadcast: Allow later probed device enter oneshot mode

Broadcast device is switched to oneshot mode in
hrtimer_switch_to_hres() -> tick_broadcast_switch_to_oneshot().
After high resolution timers are enabled, new installed
broadcast device has no chance to switch mode.

This issue happens in below situation:
In order to make broadcast clock source driver build as module,
use module_platform_driver() to replace TIMER_OF_DECLARE().
This will make clock source driver probed later than
high resolution timers enabled.

Signed-off-by: Jindong Yue <jindong.yue@....com>
---
 kernel/time/tick-broadcast.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index e51778c312f1..f38a7544cb5b 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -47,6 +47,7 @@ static inline void tick_resume_broadcast_oneshot(struct clock_event_device *bc)
 static inline void tick_broadcast_oneshot_offline(unsigned int cpu) { }
 # endif
 #endif
+static void tick_handle_oneshot_broadcast(struct clock_event_device *dev);
 
 /*
  * Debugging: see timer_list.c
@@ -115,8 +116,20 @@ 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)
+	if (dev->features & CLOCK_EVT_FEAT_ONESHOT) {
 		tick_clock_notify();
+
+		/*
+		 * If new broadcast device is installed after high resolution
+		 * timers enabled, it can not switch to oneshot mode anymore.
+		 * Here give it a chance.
+		 */
+		if (tick_broadcast_oneshot_active() &&
+		    dev->event_handler != tick_handle_oneshot_broadcast) {
+			tick_broadcast_switch_to_oneshot();
+		}
+	}
+
 }
 
 /*
-- 
2.17.1