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

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Date:	Sat, 23 May 2009 01:04:12 +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 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?

-- 
Kyuwon (규원)
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