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

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Message-ID: <4d34a0a70905221603g785f5b78h330249ff258dbfdd@mail.gmail.com>
Date:	Sat, 23 May 2009 08:03:50 +0900
From:	Kim Kyuwon <chammoru@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] PM: suspend_device_irqs(): don't disable wakeup IRQs

On Sat, May 23, 2009 at 7:29 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Saturday 23 May 2009, Kim Kyuwon wrote:
>> On Sat, May 23, 2009 at 6:23 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> > On Friday 22 May 2009, Kim Kyuwon wrote:
>> >> On Wed, May 6, 2009 at 8:27 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> >> > On Wednesday 06 May 2009, Kevin Hilman wrote:
>> >> >> Arve Hjønnevåg <arve@...roid.com> writes:
>> >> >>
>> >> >> > On Tue, May 5, 2009 at 8:52 AM, Kevin Hilman
>> >> >> > <khilman@...prootsystems.com> wrote:
>> >> >> >> Andrew Morton <akpm@...ux-foundation.org> writes:
>> >> >> >>
>> >> >> >>> On Mon,  4 May 2009 17:27:04 -0700 Kevin Hilman <khilman@...prootsystems.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?
>
> No, the changes are not going to be reverted.  In fact things should have been
> done like this already much earlier.
>
> Now, do you have any particular example of a problem related to these changes
> or is it only a theoretical issue?

I'd CCing you when I'm sending a mail for this particular example of a example.
http://markmail.org/thread/fvt7d62arofon5xx

Regards,
Kyuwon
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