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

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Message-ID: <d6200be20905071452t3efb67gffd4de5332e83e73@mail.gmail.com>
Date:	Thu, 7 May 2009 14:52:03 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Kevin Hilman <khilman@...prootsystems.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

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.

> 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.

> Note that even though __disable_irq() also calls irq_chip->disable, it
> is quite common for the irq_chip not to provide a disable hook in
> which case the IRQ is never masked/disabled in hardware before going
> into suspend.
>
> Signed-off-by: Kevin Hilman <khilman@...prootsystems.com>
> ---
>  kernel/irq/manage.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 2734eca..c786820 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -190,6 +190,13 @@ void __disable_irq(struct irq_desc *desc, unsigned int irq, bool suspend)
>                if (!desc->action || (desc->action->flags & IRQF_TIMER))
>                        return;
>                desc->status |= IRQ_SUSPENDED;
> +
> +               /*
> +                * Lazy disable: handles case where lazy disable in
> +                * handler doesn't happen before suspend.
> +                */
> +               if (desc->status & IRQ_DISABLED)
> +                       desc->chip->mask(irq);
>        }
>
>        if (!desc->depth++) {
> --
> 1.6.2.2
>
> --
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-- 
Arve Hjønnevåg
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