linux-kernel - Re: [RFC][PATCH 2/2] PM: Rework handling of interrupts during suspend-resume

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Message-Id: <200902262330.52390.rjw@sisk.pl>
Date:	Thu, 26 Feb 2009 23:30:51 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Len Brown <lenb@...nel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH 2/2] PM: Rework handling of interrupts during suspend-resume

On Thursday 26 February 2009, Linus Torvalds wrote:
> 
> On Thu, 26 Feb 2009, Rafael J. Wysocki wrote:
> > 
> > Well, how exactly the $subject patch does cause this problem to happen?
> 
> Rafael, the problem is that if an interrupt happens while it's disabled - 
> but before the CPU has actually turned all interrupts off - the CPU will 
> ACK the interrupt (but just set a flag for it being PENDING), so now the 
> chipset logic around it will not see it as pending any more, so now the 
> chipset won't auto-wake the CPU immediately (or more likely, it won't 
> even suspend it).

Ah, I see now, thanks.

> It's trivial to fix multiple ways, so I wouldn't worry. The most trivial 
> way is to just have some sysdev drievr code simply do something like
> 
>   static int sysdev_suspend()
>   {
> 	for_each_irq(irq,desc) {
> 		if (!(desc->flags & IRQF_WAKE))
> 			continue;
> 		if (desc->flags & IRQ_PENDING)
> 			return -EBUSY;
> 	}
> 	return 0;
>   }
> 
> and that should automatically mean that if any irq is pending, the suspend 
> will fail and we'll immediately wake up again.

Yeah.

Thanks,
Rafael
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