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

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Date:	Tue, 05 May 2009 17:38:43 -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:
>>> 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.  
>
> Hmm, that's not normally what I think of as disabled.  ;)
>
>> 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.

So just as a test, I just removed the 'disable' hook from my platforms
irq_chip and this allows me to wakeup without using my proposed patch,
although I'm not sure it is the right behavior either.

The 'struct irq_chip' comments are a bit misleading here as it says

 * @disable:		disable the interrupt (defaults to chip->mask if NULL)

And since my irq_chip->disable was doing basically the same thing as
my irq_chip->mask, I didn't expect it to change behavior.  But in
kernel/irq/chip.c, disable gets set to an empty default_disable if the
irq_chip's version is NULL.

The result is that if irq_chip->disable == NULL, suspend_device_irqs() is a 
big NOP, albiet one that does lots of locking. :)

So, should the irq_chip code be fixed to match the comment?  Something
like the patch below?  If I fix the IRQ chip code, then I'm back to
needing my patch since my irq_chip mask function still masks the IRQ
at the hardware.

Kevin


commit f9b534f23ac7835eead99fb0a9cec7c505fe1e85
Author: Kevin Hilman <khilman@...prootsystems.com>
Date:   Tue May 5 17:32:59 2009 -0700

    IRQ: chip->disable should default to chip->mask if NULL
    
    The struct irq_chip comments in <linux/irq.h> state:
    
     * @disable:	disable the interrupt (defaults to chip->mask if NULL)
    
    However, the code in kernel/irq/chip.c does otherwise by setting
    a NULL disable hook to an empty default_disable function.
    
    This patch makes the default_disable function call the ->mask hook
    to match the comments.
    
    Signed-off-by: Kevin Hilman <khilman@...prootsystems.com>

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index c687ba4..0fb690a 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -238,6 +238,10 @@ static void default_enable(unsigned int irq)
  */
 static void default_disable(unsigned int irq)
 {
+	struct irq_desc *desc = irq_to_desc(irq);
+
+	desc->chip->mask(irq);
+	desc->status |= IRQ_MASKED;
 }
 
 /*
--
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