linux-kernel - Re: [RFC][PATCH 1/4] PM: Rework handling of interrupts during suspend-resume (rev. 4)

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Date:	Tue, 3 Mar 2009 00:27:12 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Arve Hjønnevåg <arve@...roid.com>,
	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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>,
	Alan Stern <stern@...land.harvard.edu>,
	Johannes Berg <johannes@...solutions.net>
Subject: Re: [RFC][PATCH 1/4] PM: Rework handling of interrupts during suspend-resume (rev. 4)

On Tuesday 03 March 2009, Arve Hjønnevåg wrote:
> On Mon, Mar 2, 2009 at 3:13 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > On Tuesday 03 March 2009, Arve Hjønnevåg wrote:
> >> On Sun, Mar 1, 2009 at 2:24 PM, Rafael J. Wysocki <rjw@...k.pl> 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.
> >> >
> >>
> >>
> >> > +void resume_device_irqs(void)
> >> > +{
> >> > +       struct irq_desc *desc;
> >> > +       int irq;
> >> > +
> >> > +       for_each_irq_desc(irq, desc)
> >> > +               if (desc->status & IRQ_SUSPENDED)
> >> > +                       enable_irq(irq);
> >> > +}
> >>
> >> I think you need to clear IRQ_SUSPENDED here, not in enable_irq.
> >
> > enable_irq() clears IRQ_SUSPENDED.  This has already been discussed btw.
> >
> 
> I'm if I missed that discussion, but enable_irq cannot know who is
> calling it and therefore cannot know if IRQ_SUSPENDED should be
> cleared.

This change has been requested by Ingo and for a reason.

Ingo, what's your opinion?

> >> > @@ -222,8 +222,9 @@ static void __enable_irq(struct irq_desc
> >> >                WARN(1, KERN_WARNING "Unbalanced enable for IRQ %d\n", irq);
> >> >                break;
> >> >        case 1: {
> >> > -               unsigned int status = desc->status & ~IRQ_DISABLED;
> >> > +               unsigned int status;
> >> >
> >> > +               status = desc->status & ~(IRQ_DISABLED | IRQ_SUSPENDED);
> >> >                /* Prevent probing on this irq: */
> >> >                desc->status = status | IRQ_NOPROBE;
> >> >                check_irq_resend(desc, irq);
> >>
> >> This only clears IRQ_SUSPENDED if the interrupt was not disabled
> >> elsewhere. If a driver calls interrupt_disable in suspend_late, but
> >> calls interrupt_enable lazily, resume_device_irqs will reenable the
> >> interrupt even though the driver has a disable reference.
> >
> > Then I'd regard the driver as buggy.
> 
> The bug is not in the driver. The driver called disable_irq once. You
> called disable_irq once, but enable_irq twice.

Please.

Can you show me a _single_ _driver_ currently in the tree doing something
like you describe in suspend_late and resume_early?  If you can't, then please
give up.

Thanks,
Rafael
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