Re: [PATCH] PM: suspend_device_irqs(): don't disable wakeup IRQs

[Kevin Hilman]

"Rafael J. Wysocki" <rjw@xxxxxxx> writes:

> On Wednesday 06 May 2009, Kevin Hilman wrote:
>> Arve Hjønnevåg <arve@xxxxxxxxxxx> writes:
>> 
>> > On Tue, May 5, 2009 at 8:52 AM, Kevin Hilman
>> > <khilman@xxxxxxxxxxxxxxxxxxx> wrote:
>> >> Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:
>> >>
>> >>> On Mon,  4 May 2009 17:27:04 -0700 Kevin Hilman <khilman@xxxxxxxxxxxxxxxxxxx> wrote:
>> >>>
>> >>>> Interrupts that are flagged as wakeup sources via set_irq_wake()
>> >>>> should not be disabled for suspend.
>> >>>>
>> >>>
>> >>> Why not?
>> >>>
>> >>
>> >> If an interrupt is a wakeup source, and it is disabled at the chip
>> >> level, it will no longer generate interrupts, and thus no longer wake
>> >> up the system.
>> >>
>> >> I'd be interested in hearing why wakeup interrupts should be disabled
>> >> during suspend.
>
> That depends on whether or not they are used for anything else than wake-up.
>
>> 
>> [...]
>> 
>> >>>
>> >>> If this fixes some bug then please provide a description of that bug?
>> >>
>> >> The bug is that on TI OMAP, interrupts that are used for wakeup events
>> >> are disabled by this code causing the system to no longer wake up.
>> >
>> > What do you do if the interrupt triggers right after your driver has
>> > returned from its late suspend hook?  
>> 
>> If it's a wakeup IRQ, I assume you want it to prevent suspend.
>> 
>> But I don't see how that can happen in the current code. IIUC, by the
>> time your late suspend hook is run, your device IRQ is already
>> disabled, so it won't trigger an interrupt that will be caught by
>> check_wakeup_irqs() anyways.
>
> My understanding of __disable_irq() was that it didn't actually disable the
> IRQ at the hardware level, allowing the CPU to actually receive the interrupt
> and acknowledge it, but preventing the device driver for receiving it.  

Hmm, that's not normally what I think of as disabled.  ;)

> Does it work differently on the affected systems?

Yes.

__disable_irq() calls the irq_chip's disable method which is platform
specific.  On OMAP, this masks the IRQ at the hardware level
preventing the CPU from seeing the interrupt.

Kevin


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