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

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Message-Id: <200905230147.16037.rjw@sisk.pl>
Date:	Sat, 23 May 2009 01:47:15 +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 Saturday 23 May 2009, Kim Kyuwon wrote:
> On Sat, May 23, 2009 at 6:25 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > 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?
> 
> That's not quite right.
> 
> For example, let's assume a keypad device is alive in suspend/resume
> state to wake up the system. Before arch_suspend_enable_irqs(), none
> of keypad irqs is dropped. It is just pending.
>
> But in your code, a few irqs are discarded due to your resume_device_irqs().

You can't say for sure they are discarded, but there's a small window in which
they can be discarded.  The question is whether it does cause problems in
practice.

Anyway, IMO the device that caused a wake-up event should be deactivated before
arch_suspend_enable_irqs() and remain inactive until its driver is actually
ready to handle interrupts generated by it.

Thanks,
Rafael
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