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

[Kim Kyuwon <chammoru@gmail.com>]

On Sat, May 23, 2009 at 6:23 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> On Friday 22 May 2009, Kim Kyuwon wrote:
>> On Wed, May 6, 2009 at 8:27 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
>> > On Wednesday 06 May 2009, Kevin Hilman wrote:
>> >> Arve Hjønnevåg <arve@android.com> writes:
>> >>
>> >> > On Tue, May 5, 2009 at 8:52 AM, Kevin Hilman
>> >> > <khilman@deeprootsystems.com> wrote:
>> >> >> Andrew Morton <akpm@linux-foundation.org> writes:
>> >> >>
>> >> >>> On Mon,  4 May 2009 17:27:04 -0700 Kevin Hilman <khilman@deeprootsystems.com> 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.  Does
>> > it work differently on the affected systems?
>>
>> Hi, Rafael.
>> Sorry for bring the old issue but please let me ask you about
>> suspend_device_irqs() function.
>>
>> __disable_irq() disables the IRQ at the hardware level in the
>> following irq_chips
>>
>> i8259A_chip
>> i8259_pic
>> i8259A_chip
>> bfin_internal_irqchip
>> crisv10_irq_type
>> crisv32_irq_type
>> h8300irq_chip
>> m_irq_chip
>> mn10300_cpu_pic_level
>> xtensa_irq_chip
>> iop13xx_msi_chip
>> msi_irq
>>
>> Because these irq_chips mask interrupts in 'disable' hook.
>>
>> Thus, your suspend_device_irqs() function disables all IRQs at the
>> hardware level on all architectures which use irq_chips listed above
>> in suspend state.
>> Is this really what you wanted?
>
> What we wanted was to resolve specific issue related to the handling of
> interrupts during suspend and resume which caused observable breakage and
> from the point of view of fixing this issue it doesn't really matter whether or
> not interrupts are masked in the disable hook.
>
>> If interrupt can wake up the system from suspend in some architectures
>> and if disable_irq_wake is not supported in these architectures, I
>> wonder if suspend_device_irqs() don't allow waking up by interrupt.
>
> I think that the platforms that may be affected by this issue will have to take
> care of it.

You changed the really important part of Linux, which may affect most
processor architectures. I think you should be careful. If some of
architectures can't take care of it (they can implement
disable_irq_wake correctly in H/W level, will you revert your changes?

Sincerely,
Kyuwon.