Re: [PATCH v2 5/6] watchdog: at91sam9: request the irq with IRQF_NO_SUSPEND

Rafael J. Wysocki
2015-03-05T15:10:23Z

On Thu, Mar 5, 2015 at 11:57 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> [...]
>
>> > > err = request_irq(wdt->irq, wdt_interrupt,
>> > > - IRQF_SHARED | IRQF_IRQPOLL,
>> > > + IRQF_SHARED | IRQF_IRQPOLL |
>> > > + IRQF_NO_SUSPEND,
>> >
>> > I'm a little confused by this. What happens if the watchdog fires when
>> > we're actually in the suspended state (when IRQF_NO_SUSPEND interrupts
>> > aren't guaranteed to be delivered).
>>
>> Why wouldn't they be delivered?
>>
>> If that's suspend-to-idle, we'll handle them normally. If that's full suspend,
>> they may not be handled at the last stage (when we run on one CPU with interrupts
>> off), but that was the case before the wakeup interrupts rework already and I'd
>> expect it to be taken into account somehow in the existing code (or if it isn't
>> taken into account, we have a bug, but it is not related to this series).
>
> There's no enable_irq_wake(wdt->irq), and I was under the impression this
> is for full suspend.

enable_irq_wake() has no effect on IRQF_NO_SUSPEND interrupts, so if the
driver uses IRQF_NO_SUSPEND, it does not need to use enable_irq_wake()
in addition to that.

Drivers using IRQF_COND_SUSPEND generally should use enable_irq_wake() too
in case they end up in a situation without sharing a NO_SUSPEND interrupt, in
which case their interrupt handlers won't be called after suspend_device_irqs(),
so they need to rely on the core to do the wakeup.

> I agree that if problematic, it's an existing bug. Given Boris's
> comments in the other thread this may just a minor semantic issue w.r.t.
> IRQF_NO_SUSPEND vs IRQF_COND_SUSPEND.

It depends on whether or not the watchdog's interrupt handler has to be
called immediately after receiving an interrupt (IRQF_NO_SUSPEND is
better then) or it can be deferred till the resume_device_irqs() time.

Rafael