linux-kernel - Re: [PATCH 2/3] IRQ: allow check_wakeup_irqs to notice level-triggered interrupts.

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Date:	Wed, 25 Apr 2012 19:39:16 +1000
From:	NeilBrown <neilb@...e.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Tony Lindgren <tony@...mide.com>,
	Russell King <linux@....linux.org.uk>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH 2/3] IRQ: allow check_wakeup_irqs to notice
 level-triggered interrupts.

On Wed, 25 Apr 2012 10:50:15 +0200 (CEST) Thomas Gleixner
<tglx@...utronix.de> wrote:

> On Wed, 25 Apr 2012, NeilBrown wrote:
> 
> > Level triggered interrupts do not cause IRQS_PENDING to be set, so
> > check_wakeup_irqs ignores them.
> > They don't need to set IRQS_PENDING as the level stays high which
> > shows that they must be pending.  However if such an interrupt fired
> > during late suspend, it will have been masked so the fact that it
> > is still asserted will not cause the suspend to abort.
> > 
> > So if any wakeup interrupt is masked, unmask it when checking wakeup
> > irqs.  If the interrupt is asserted, suspend will abort.
> > 
> > Signed-off-by: NeilBrown <neilb@...e.de>
> > ---
> > 
> >  kernel/irq/pm.c |    6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/kernel/irq/pm.c b/kernel/irq/pm.c
> > index 15e53b1..0d26206 100644
> > --- a/kernel/irq/pm.c
> > +++ b/kernel/irq/pm.c
> > @@ -106,6 +106,12 @@ int check_wakeup_irqs(void)
> >  		if (irqd_is_wakeup_set(&desc->irq_data)) {
> >  			if (desc->istate & IRQS_PENDING)
> >  				return -EBUSY;
> > +			if (irqd_irq_masked(&desc->irq_data))
> > +				/* Probably a level interrupt
> > +				 * which fired recently and was
> > +				 * masked
> > +				 */
> > +				unmask_irq(desc);
> 
> Oh no. We don't unmask unconditionally. What about an interrupt which
> is disabled, has no handler ..... ? That needs more thought.

If there is no handler, then irqd_is_wakeup_set() should fail should it not?

For disabled: would it be OK to check desc->depth?
Something like:
     if (desc->depth == 1 && (desc->state & IRQS_SUSPENDED) &&
         irqd_irq_masked(&desc->irq_data))
              unmask_irq(desc);

??

Thanks,
NeilBrown

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