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

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Date:	Mon, 2 Mar 2009 15:18:57 -0800
From:	Arve Hjønnevåg <arve@...roid.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	"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 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.

>> > @@ -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.

-- 
Arve Hjønnevåg
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