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Date: Fri, 6 Mar 2015 13:10:26 +0000
From: Mark Rutland <mark.rutland@arm.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
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Subject: Re: [PATCH v2 5/6] watchdog: at91sam9: request the irq with
 IRQF_NO_SUSPEND
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> >> > We seem to be conflating some related properties:
> >> >
> >> > [a] The IRQ will be left unmasked.
> >> > [b] The IRQ will be handled immediately when taken.
> >> > [c] The IRQ will wake the system from suspend.

[...]

> > Considering that the use-case of a watchdog is to alert us to something
> > going hideously wrong in the kernel, we want to handle the IRQ after
> > executing the smallest amount of kernel code possible. For that, they
> > need to have their handlers to be called "immediately" outside of the
> > arch_suspend_disable_irqs() ... arch_suspend_enable_irqs() window, and
> > need to be enabled during suspend to attempt to catch bad wakeup device
> > configuration.
> >
> > I think it's possible (assuming the caveats on [b] above) to provide
> > [a,b,c] for this case.
> 
> OK
> 
> But in this case the request_irq() passing IRQF_NO_SUSPEND *and* requiring
> enable_irq_wake() in addition to that needs a big fat comment explaining the
> whole thing or we'll forget about the gory details at one point and no one will
> know what's going on in there.

Agreed.

I'd expect an IRQF_SW_WATCHDOG or something to that effect should also
be required for that case.

Thanks,
Mark.