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Date: Wed, 25 Feb 2009 00:09:35 +0100
From: Ingo Molnar <mingo@elte.hu>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Jeremy Fitzhardinge <jeremy@goop.org>,
       pm list <linux-pm@lists.linux-foundation.org>,
       Len Brown <lenb@kernel.org>, Jesse Barnes <jbarnes@virtuousgeek.org>,
       Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC][PATCH 2/2] PM: Rework handling of interrupts during
	suspend-resume
Message-ID: <20090224230935.GA15165@elte.hu>
References: <200902221837.49396.rjw@sisk.pl> <200902242342.07721.rjw@sisk.pl> <alpine.LFD.2.00.0902241449221.3111@localhost.localdomain> <200902250007.13069.rjw@sisk.pl>
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* Rafael J. Wysocki <rjw@sisk.pl> wrote:

> On Tuesday 24 February 2009, Linus Torvalds wrote:
> > 
> > On Tue, 24 Feb 2009, Rafael J. Wysocki wrote:
> > >
> > > > The only safe way on x86 to shutdown a level triggered ioapic irq
> > > > outside of irq context is for the driver to program the hardware to
> > > > not generate an irq.
> > > 
> > > Well, that changes things quite a bit, because it means we can't change the
> > > suspend-resume sequence in a way we thought we could without fixing all
> > > drivers first, but this is exactly what we'd like to avoid by changing the
> > > core.
> > 
> > Calling "disable_irq()" is perfectly fine.
> > 
> > What is not possible on that broken IO-APIC (among other 
> > things) is to actually turn the interrupts off at the apic 
> > (ie the whole ->shutdown() thing). But that's not what we 
> > even want to do. What we care about is just disabling the 
> > interrupt from a drievr perspective.
> > 
> > IOW, the patches I have seen are fine, and all the comments 
> > from Eric are just confusion about what we want done.
> 
> Ah, OK.  Thanks for the explanation, I got confused too.
> 
> > WE DO NOT WANT TO TURN OFF THE IO-APIC. That may or may 
> > happen later, but that's totally unrelated to this whole 
> > "suspend_device_irq()" thing.
> 
> Yeah.

We definitely dont want to turn off x86 IO-APICs - the timer IRQ 
goes via one of them.

	Ingo