linux-kernel - Re: [linux-pm] [RFC][PATCH][1/8] PM: Rework handling of interrupts during suspend-resume (rev. 5)

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Message-ID: <Pine.LNX.4.44L0.0903072248030.8870-100000@netrider.rowland.org>
Date:	Sat, 7 Mar 2009 22:53:31 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Arve Hjønnevåg <arve@...roid.com>
Subject: Re: [linux-pm] [RFC][PATCH][1/8] PM: Rework handling of interrupts
 during suspend-resume (rev. 5)

On Sat, 7 Mar 2009, Rafael J. Wysocki wrote:

> > One thing about this isn't clear: the distinction between "wake-up" 
> > interrupts and other interrupts.
> > 
> > In an ideal world, the only pending interrupts during sysdev_suspend
> > would be wake-up interrupts, because drivers would have prevented their
> > devices from generating any other kind of IRQ and would have done all
> > the necessary synchronization as part of their suspend (_not_
> > suspend_late) methods.  Thus there would be no need to distinguish
> > between wake-up and non-wake-up interrupts.
> > 
> > So perhaps you're worried about drivers that aren't sufficiently
> > clever.  Or is something deeper going on?
> 
> Some drivers leave interrupts enabled during suspend on purpose and mark
> them as "wake-up interrupts" so that the platform can abort suspend if any
> of them is pending at the time the "enter suspend" hook is called (this doesn't
> happen on x86 AFAICS).
> 
> However, after the $subject patch the CPU will ACK those interrupts if they
> happen between suspend_device_irqs() and local_irq_disable(), so the platform
> won't see them as pending.  Instead, they will have IRQ_PENDING set in
> desc->status, so we check if this is the case.

You didn't answer my question.  Why bother to distinguish between 
"wake-up" interrupts and non-"wake-up" interrupts?

In other words, why not simply abort the suspend if IRQ_PENDING is set
for _any_ interrupt during sysdev_suspend()?

Alan Stern

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