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

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Message-Id: <200905300135.07103.rjw@sisk.pl>
Date:	Sat, 30 May 2009 01:35:05 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Kim Kyuwon <q1.kim@...sung.com>
Cc:	Kim Kyuwon <chammoru@...il.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 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.  The only problem I see is that the drivers may expect their
->resume_noirq() callbacks to be executed first.

Thanks,
Rafael
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