linux-kernel - Re: [PATCH 2/2] rtc: Avoid accumulating time drift in suspend/resume

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Message-ID: <1306977263.11492.32.camel@work-vm>
Date:	Wed, 01 Jun 2011 18:14:23 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] rtc: Avoid accumulating time drift in
 suspend/resume

On Wed, 2011-06-01 at 17:54 -0700, Arve Hjønnevåg wrote:
> On Tue, May 31, 2011 at 11:07 PM, John Stultz <john.stultz@...aro.org> wrote:
> > +       /*
> > +        * Since these RTC suspend/resume handlers are not called
> > +        * at the very end of suspend or the start of resume,
> > +        * some run-time may pass on either sides of the sleep time
> > +        * so subtract kernel run-time between rtc_suspend to rtc_resume
> > +        * to keep things accurate.
> > +        */
> > +       sleep_time = timespec_sub(sleep_time,
> > +                       timespec_sub(new_system, old_system));
> 
> What happens if sleep_time is negative? I think this need to be
> clamped to 0 to avoid backwards jumps when you wake up more than once
> without the rtc advancing.

Good thought! Although that will be easier to catch in
timekeeping_inject_sleeptime(), so I might add it there.

Thanks for the review!
-john



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