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

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Date:	Fri, 20 Nov 2015 11:29:21 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	zhuo-hao.lee@...el.com
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>, zhuohao.lee82@...il.com
Subject: Re: [PATCH v3] alarmtimer: fix unexpected rtc interrupt when system
 resume from S3

On Tue, Nov 17, 2015 at 4:08 AM,  <zhuo-hao.lee@...el.com> wrote:
> From: zhuo-hao <zhuo-hao.lee@...el.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.

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.

thanks
-john
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