linux-kernel - Re: [PATCH] genirq: ensure IRQs are lazy disabled before suspend

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Message-ID: <87vdo7fh1t.fsf@deeprootsystems.com>
Date:	Mon, 11 May 2009 14:47:26 -0700
From:	Kevin Hilman <khilman@...prootsystems.com>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	linux-pm@...ts.linux-foundation.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] genirq: ensure IRQs are lazy disabled before suspend

Arve Hjønnevåg <arve@...roid.com> writes:

> 2009/5/8 Kevin Hilman <khilman@...prootsystems.com>:
>> Arve Hjønnevåg <arve@...roid.com> writes:
>>
>>> On Thu, May 7, 2009 at 9:19 AM, Kevin Hilman
>>> <khilman@...prootsystems.com> wrote:
>>>> From a3f359c66bd0ae1bb2603e7cf120d9d4d68591b7 Mon Sep 17 00:00:00 2001
>>>> From: Kevin Hilman <khilman@...prootsystems.com>
>>>> Date: Wed, 6 May 2009 16:00:07 -0700
>>>> Subject: [PATCH] genirq: ensure IRQs are lazy disabled before suspend
>>>>
>>>> In commit 76d2160147f43f982dfe881404cfde9fd0a9da21, the default
>>>> behavior of disable_irq() was changed to delay the disable until it is
>>>> next handled.
>>>>
>>>> However, this leaves open the possibility that the system can go into
>>>> suspend with an interrupt enabled.  For example, if a driver calls
>>>> disable_irq() in its suspend_hook there's now a possibility that the
>>>> system is suspended before the lazy disable happens.
>>>>
>>>> The result is an unwanted wakeup from suspend if the IRQ is capable of
>>>> waking the system (common on embedded SoCs.)
>>>
>>> If the interrupt contoller uses the same enable register for wakeup
>>> and interrupts, I think it is the responsibility of the platform code,
>>> not individual drivers, to disable the interrupts that are not marked
>>> for wakeup before entering suspend.
>>
>> I agree, for wakeup interrupts, drivers should use
>> [set|disable]_irq_wake() and the platform code should handle this.
>>
>> I used wakeup interrupts in this description as an example which
>> turned out to be a bad example.  The 2nd version of this patch I
>> posted, I removed the reference to wakeup interrupts in favor of just
>> talking about the delayed disable piece.
>>
>> But ignoring wakup interrupts, would you agree that the delayed
>> disable of an interrupt should not wait until after resume?
>>
>
> No. The platform code needs to turn off interrupts that are not wakeup
> interrupts anyway, so there is not much point in disabling some
> interrupts early. Also, if the interrupt in question is not a wakeup
> interrupt you leave it in a state where it does not detect an edge. A
> driver that enables its hardware in resume, then unmasks the interrupt
> would loose an interrupt that triggered between enabling the hardware
> and unmasking the interrupt.

Got it.  Thanks for your (repeated) explanations.  I understand now
your reasons for allowing the interrupt to remain across suspend.  I
will modify my platform to rely on [enable|disable]_irq_wake() in
addition to ensuring platform code is disabling non wakup IRQs.

>>>> This patch ensures that the lazy disable is done, and masked by
>>>> the irq_chip before the system goes into suspend.
>>>
>>> This will create a window where wakeup interrupts can be lost if the
>>> driver has masked the interrupt (by calling disable_irq). If the
>>> hardware does not allow edge detection on disabled interrupts (the msm
>>> platform has this limitation) then this change will turn off the edge
>>> detection. If suspend_ops->enter does not turn the interrupt (and edge
>>> detection) back on (without this change it may never need to turn on
>>> any interrupt) it will not wakeup at all.
>>
>> Not sure I follow you here...
>>
>> It seems like you're relying on the delayed disable to wait until
>> after resume so that disabled interrupts can wake the system.  How
>> did this work before the delayed disable patch?
>>
>
> It did not.
>
>> If the interrupt is being used as a wakeup, why would anyone be
>> calling disable_irq()?
>>
>
> Drivers call disable_irq to make sure their interrupt handler does not
> get called. A driver may not be able take interrupts after its suspend
> hook has been called. If it calls disable_irq on a wakeup interrupt
> then this interrupt should abort suspend or wake up from suspend. The
> driver will then see the interrupt when it call enable_irq in its
> resume handler.

OK.

Kevin
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