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

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Message-ID: <4d34a0a70905300034q1dee8febl60b5213082e3a5d1@mail.gmail.com>
Date:	Sat, 30 May 2009 16:34:38 +0900
From:	Kim Kyuwon <chammoru@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Kim Kyuwon <q1.kim@...sung.com>,
	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>,
	Kevin Hilman <khilman@...prootsystems.com>
Subject: Re: [PATCH] PM: suspend_device_irqs(): don't disable wakeup IRQs

On Sat, May 30, 2009 at 8:35 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Monday 25 May 2009, Kim Kyuwon wrote:
>> Rafael J. Wysocki wrote:
>> > On Saturday 23 May 2009, Kim Kyuwon wrote:
>> >> On Sat, May 23, 2009 at 7:29 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> >>> On Saturday 23 May 2009, Kim Kyuwon wrote:
>> > [--snip--]
>> >>>> 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
>> >
>> > Well, as I said above, reverting the changes that introduced
>> > [suspend|resume]_device_irqs() is not an option, becuase it was the only sane
>> > way to achieve the goal they were added for.  So, we need to fix the wake-up
>> > problem on your platform with the assumption that
>> > [suspend|resume]_device_irqs() are going to stay.
>> >
>> > For starters, would it be possible to teach the 'disable' hook of your
>> > platform's interrupt controller not to mask the IRQs that have both
>> > IRQ_WAKEUP and IRQ_SUSPENDED set?  That apparently would work around the
>> > wake-up interrupts problem.
>>
>> Thank you for considering this issue and spending your time. In order to
>> make your idea work, we need to add a dummy 'set_wake' hook which
>> returns always zero. Anyway, IMO, I think your idea is good to work
>> around this problem. But Kevin Hilman(OMAP PM Maintainer) would make
>> final decision.
>>
>> Buy the way, how can you handle the problem that a few interrupt are
>> discarded in a small window? I can be sure they are discarded, because I
>> have debugged defects which generate in sleep/resume state hundreds of
>> times on ARM Processors(PXA310, S3C6410, OMAP3430). Wake-up interrupts
>> are generated as soon as arch_suspend_enable_irqs() invoked.
>
> Sorry for the delayed response.
>
> If the wake-up interrupts are not masked, they will be delivered to the drivers
> as soon as arch_suspend_enable_irqs() has run.  So, if the drivers are able to
> handle them at this point (ie. before resume_device_irqs() is called), they
> won't be lost.

Thank you for your response!

Your suspend_device_irqs() disables all IRQs(except timer IRQ) while
entering suspend. i.e. Before invoking resume_device_irqs() or
resume_noirq callback, all IRQs(except timer IRQ) is in IRQ_DISABLED
status. Right?
But if an IRQ is in  IRQ_DISABLED status, its interrupt handler can be
invoked. (As you know, all IRQs with IRQ_DISABLE are not handled in
handle_level_irq function). Thus, even if the wake-up interrupts are
not masked, the drivers are not able to handle interrupts, because the
interrupt handler can't be invoked due to IRQ_DISABLED set by
suspend_device_irqs().

> The only problem I see is that the drivers may expect their
> ->resume_noirq() callbacks to be executed first.

resume_noirq() callbacks are also invoked after arch_suspend_enable_irqs().

Regards,
Kyuwon
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