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

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Date:	Sun, 8 Mar 2009 22:37:07 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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>,
	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 Sunday 08 March 2009, Alan Stern wrote:
> On Sun, 8 Mar 2009, Linus Torvalds wrote:
> 
> > On Sat, 7 Mar 2009, Alan Stern wrote:
> > > 
> > > 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()?
> > 
> > .. because some drivers might not actually shut down the hardware until 
> > they get to "suspend_late"? If even then, for that matter - a driver may 
> > simply not care, knowing that the hardware will be powered off, and will 
> > be re-initialized at resume.
> > 
> > The thinking that you have to shut your hardware down at "->suspend()" 
> > time is a _disease_. There are literally classes of hardware out there 
> > where that would be an outright _bug_, like for a PCI bridge device. For 
> > many devices, "suspend()" has to be the phase where you shut down the 
> > _external_ stuff (eg for a disk controller, it's when you'd flush and stop 
> > your disks), but the controller itself may well be alive until later.
> 
> Yes, certainly.  I agree completely.
> 
> But there is a difference between shutting down the hardware and merely
> preventing it from generating interrupt requests.  If a device remains
> capable of generating IRQs after its driver's suspend method has run,
> the driver runs the risk of having its handler called at a time when it
> isn't prepared to cope correctly.  Of course, this will depend on the
> details of how the driver is written.
> 
> There have been examples in the past of devices that, for one reason or
> another, _did_ generate IRQs at inconvenient times.  The hardware or
> the BIOS may have done improper initialization, for example.  On a
> shared IRQ this led to interrupt storms.

Well, we're now trying to fix exactly this problem. :-)

>  IIRC, the solution was to add a PCI quirk routine to disable IRQ generation
>  at an early stage.   Didn't e100 have this problem?

I don't remember, sorry.

Thanks,
Rafael
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