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.4.44L0.0903071143340.5732-100000@netrider.rowland.org>
Date:	Sat, 7 Mar 2009 11:51:19 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	LKML <linux-kernel@...r.kernel.org>,
	<Arve@...p1.linux-foundation.org>,
	Jeremy Fitzhardinge <jeremy@...p.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>
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:

> 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?

Alan Stern

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