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

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Message-ID: <871vr22upr.fsf@deeprootsystems.com>
Date:	Wed, 06 May 2009 07:04:48 -0700
From:	Kevin Hilman <khilman@...prootsystems.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] PM: suspend_device_irqs(): don't disable wakeup IRQs

Kevin Hilman <khilman@...prootsystems.com> writes:

> "Rafael J. Wysocki" <rjw@...k.pl> writes:
>
>> On Wednesday 06 May 2009, Kevin Hilman wrote:

[...]

>>> 
>>> [...]
>>> 
>>> >>>
>>> >>> 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?
>
> Yes.
>
> __disable_irq() calls the irq_chip's disable method which is platform
> specific.  On OMAP, this masks the IRQ at the hardware level
> preventing the CPU from seeing the interrupt.

Looking at x86, the i8259 disable hook also seems to mask the IRQ at
the PIC level.

The various IO-APIC irq_chips do not have a disable hook so the
__disable_irq() here is a NOP.

Kevin
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