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

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Date:	Sat, 30 May 2009 16:40:31 +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 4:34 PM, Kim Kyuwon <chammoru@...il.com> wrote:
> 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

Sorry: *Can't 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
>



-- 
Kyuwon (규원)
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