[PATCH v3] alarmtimer: fix unexpected rtc interrupt when system resume from S3

[zhuo-hao.lee@intel.com]

From: zhuo-hao <zhuo-hao.lee@intel.com>

Before the system go to suspend (S3), if user create a timer with clockid
CLOCK_REALTIME_ALARM/CLOCK_BOOTTIME_ALARM and set a "large" timeout value
to this timer. The function alarmtimer_suspend will be called to setup
a timeout value to RTC timer to avoid the system sleep over time. However,
if the system wakeup early than RTC timeout, the RTC timer will not be cleared.
And this will cause the hpet_rtc_interrupt come unexpectedly until the RTC
timeout. To fix this problem, just adding alarmtimer_resume to cancel the
RTC timer.

This was noticed because the HPET RTC emulation fires an interrupt every
16ms(=1/2^DEFAULT_RTC_SHIFT) up to the point where the alarm time is reached.
This program always hits this situation(https://lkml.org/lkml/2015/11/8/326),
if system wake up earlier than alarm time.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Zhuo-hao Lee <zhuo-hao.lee@intel.com>
---
 kernel/time/alarmtimer.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 7fbba63..e840ed8 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -271,11 +271,27 @@ static int alarmtimer_suspend(struct device *dev)
 		__pm_wakeup_event(ws, MSEC_PER_SEC);
 	return ret;
 }
+
+static int alarmtimer_resume(struct device *dev)
+{
+	struct rtc_device *rtc;
+
+	rtc = alarmtimer_get_rtcdev();
+	if (rtc)
+		rtc_timer_cancel(rtc, &rtctimer);
+	return 0;
+}
+
 #else
 static int alarmtimer_suspend(struct device *dev)
 {
 	return 0;
 }
+
+static int alarmtimer_resume(struct device *dev)
+{
+	return 0;
+}
 #endif
 
 static void alarmtimer_freezerset(ktime_t absexp, enum alarmtimer_type type)
@@ -800,6 +816,7 @@ out:
 /* Suspend hook structures */
 static const struct dev_pm_ops alarmtimer_pm_ops = {
 	.suspend = alarmtimer_suspend,
+	.resume = alarmtimer_resume,
 };
 
 static struct platform_driver alarmtimer_driver = {
-- 
2.1.2