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

From: John Stultz
Date: Fri Nov 20 2015 - 14:29:26 EST

On Tue, Nov 17, 2015 at 4:08 AM, <zhuo-hao.lee@xxxxxxxxx> wrote:
> From: zhuo-hao <zhuo-hao.lee@xxxxxxxxx>
> 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(,
> if system wake up earlier than alarm time.

So thanks for the extra context here, and again I don't have an
objection to this patch.

Although from the earlier discussion it still isn't quite clear to me:
Why must the HPET RTC emulation need to fire the alarm every 16ms? Is
that not something that can be fixed?

I just want to make sure we're not hiding a deeper issue.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at