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

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Date:	Thu, 26 Feb 2009 16:00:52 -0800
From:	Arve Hjønnevåg <arve@...roid.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Thu, Feb 26, 2009 at 3:10 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Thursday 26 February 2009, Arve Hjønnevåg wrote:
>> On Thu, Feb 26, 2009 at 2:10 PM, Linus Torvalds
>> <torvalds@...ux-foundation.org> 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).
>> >
>> > 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.
>> >
>> > It looks trivial, and I don't understand why Arve can't just do the sysdev
>> > thing.
>>
>> I can. My point is that the patch breaks our existing code.
>
> Is that a mainline kernel code?

No, the msm suspend support has not been merged.

>
>> If anyone else uses edge triggered wakeup interrupt it may break from them as
>> well. The main question if this should be fixed separately for every
>> platform that needs it, or if pending wakeup interrupts should always
>> abort sleep.
>
> Well, I'm not really sure if this is the problem.  In fact the problem is that
> you have a regular device the interrupt of which can be a wake-up one.  I think

Is that not a common case and what enable_irq_wake is for?

> the problem wouldn't have existed at all if it had been a sysdev.  Is that
> correct?

How many sysdevs use interrupts?

I found may drivers in the mainline kernel that use enable_irq_wake,
but I did not see any that handle this race condition.

-- 
Arve Hjønnevåg
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