linux-kernel - Re: + rtc-disable-hpet-emulation-on-suspend.patch added to -mm tree

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Date:	Wed, 14 Oct 2009 08:35:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Maxim Levitsky <maximlevitsky@...il.com>
Cc:	akpm@...ux-foundation.org, mm-commits@...r.kernel.org,
	david-b@...bell.net, hpa@...or.com, rjw@...k.pl,
	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: + rtc-disable-hpet-emulation-on-suspend.patch added to -mm tree


* Maxim Levitsky <maximlevitsky@...il.com> wrote:

> On Wed, 2009-10-14 at 07:56 +0200, Ingo Molnar wrote:
> > * akpm@...ux-foundation.org <akpm@...ux-foundation.org> wrote:
> > 
> > > ------------------------------------------------------
> > > Subject: rtc: disable hpet emulation on suspend
> > > From: Maxim Levitsky <maximlevitsky@...il.com>
> > > 
> > > I noticed that rtc wont generate interrupts after a resume from disk.
> > > Here hpet rtc emulation is used.
> > > 
> > > Problem is that rtc hpet comparator, isn't reinitialized after resume.
> > > Easiest way to solve this, is always mask all hpet interrupts on suspend
> > > This is triggered, when suspending with alarm set.
> > > 
> > > 
> > > Otherwise, hpet driver will think it doesn't need to reinitialize
> > > the rtc comparator, thus rtc interrupts won't work.
> > > 
> > > This emulation isn't need for wakealarm.
> > 
> > > -		hpet_mask_rtc_irq_bit(mask);
> > >  
> > > +		/* shut down hpet emulation - we don't need it for alarm */
> > > +		hpet_mask_rtc_irq_bit(RTC_PIE|RTC_AIE|RTC_UIE);
> > >  		cmos_checkintr(cmos, tmp);
> > 
> > Would be nice to also unconditionally reinitialize the hpet/rtc after 
> > resume - regardless of what state we left it in.
> 
> I think this is already done.
> Problem was that rtc driver was leaving the RTC_AIE, thus breaking the
> initialization.
> 
> If there are no users of hpet on suspend, (periodic,alarm,update), then
> it won't be initialized on resume (only rtc comparator part, other parts
> are initialized correctly nowadays) but as soon as anybody start using
> it, it will be.
>  
> 
> > 
> > Also, are you sure this does not break things like 
> > CONFIG_PM_TEST_SUSPEND=y which rely on wakealarm?
> 
> 
> This shouldn't break anything. hpet irqs aren't used for the actual
> alarm.
> 
> In fact I used a script to loop over real hibernation cycles, and it 
> works with or without this patch.
> 
> But with this patch, hwclock works after a resume.

Excellent - thanks!

	Ingo
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