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

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Message-Id: <200905222325.27950.rjw@sisk.pl>
Date:	Fri, 22 May 2009 23:25:27 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Kim Kyuwon <chammoru@...il.com>
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>,
	Kevin Hilman <khilman@...prootsystems.com>
Subject: Re: [PATCH] PM: suspend_device_irqs(): don't disable wakeup IRQs

On Friday 22 May 2009, Kim Kyuwon wrote:
> On Fri, May 22, 2009 at 11:53 AM, Kim Kyuwon <chammoru@...il.com> 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?
> >
> > 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.
> >
> > Regards,
> > Kyuwon
> >
> 
> I saw resume_device_irqs() is invoked after arch_suspend_enable_irqs()
> in your resume code.
> So in this gap between resume_device_irqs() and
> arch_suspend_enable_irqs(), a few interrupts would be discarded.
> i.e, a few data would be lost.
> 
> If keypad wake up the system, first key pressed information would be lost.
> If I2C, USB, SPI, UART wake up the system, first a few data would be lost.
> 
> Did you also consider this issue?

I think it would happen anyway with the old code, wouldn't it?

Best,
Rafael
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