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

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Date:	Sat, 7 Mar 2009 18:56:35 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	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 Saturday 07 March 2009, Alan Stern wrote:
> On Sat, 7 Mar 2009, Rafael J. Wysocki wrote:
> 
> > From: Rafael J. Wysocki <rjw@...k.pl>
> > 
> > Introduce two helper functions allowing us to prevent device drivers
> > from getting any interrupts (without disabling interrupts on the CPU)
> > during suspend (or hibernation) and to make them start to receive
> > interrupts again during the subsequent resume, respectively.  These
> > functions make it possible to keep timer interrupts enabled while the
> > "late" suspend and "early" resume callbacks provided by device
> > drivers are being executed.
> > 
> > Use these functions to rework the handling of interrupts during
> > suspend (hibernation) and resume.  Namely, interrupts will only be
> > disabled on the CPU right before suspending sysdevs, while device
> > drivers will be prevented from receiving interrupts, with the help of
> > the new helper function, before their "late" suspend callbacks run
> > (and analogously during resume).
> > 
> > In addition, since the device interrups are now disabled before the
> > CPU has turned all interrupts off and the CPU will ACK the interrupts
> > setting the IRQ_PENDING bit for them, check in sysdev_suspend() if
> > any wake-up interrupts are pending and abort suspend if that's the
> > case.
> 
> 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.

Thanks,
Rafael


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