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

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Message-ID: <4d34a0a70905221532l772d03b6gb6436f0b8eb10274@mail.gmail.com>
Date:	Sat, 23 May 2009 07:32:22 +0900
From:	Kim Kyuwon <chammoru@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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 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().

Regards,
Kyuwon
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