linux-kernel - Re: [PATCH] genirq: describe IRQF_COND

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Date:	Wed, 04 Mar 2015 22:55:58 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] genirq: describe IRQF_COND_SUSPEND

On Wednesday, March 04, 2015 08:00:40 PM Mark Rutland wrote:
> With certain restrictions it is possible for a wakeup device to share
> and IRQ with an IRQF_NO_SUSPEND user, and the warnings introduced by
> commit cab303be91dc47942bc25de33dc1140123540800 are spurious. The new
> IRQF_COND_SUSPEND flag allows drivers to tell the core when these
> restrictions are met, allowing spurious warnings to be silenced.
> 
> This patch documents how IRQF_COND_SUSPEND is expected to be used,
> updating some of the text now made invalid by its addition.
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Boris Brezillon <boris.brezillon@...e-electrons.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  Documentation/power/suspend-and-interrupts.txt | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> As promised previously, take IRQF_COND_SUSPEND into account in the
> documentation.
> 
> Rafael, does this look OK to you?

Yes, it does, thanks!

I'll queue it up along with the rest of the IRQF_COND_SUSPEND patches.


> diff --git a/Documentation/power/suspend-and-interrupts.txt b/Documentation/power/suspend-and-interrupts.txt
> index 50493c9..8afb29a 100644
> --- a/Documentation/power/suspend-and-interrupts.txt
> +++ b/Documentation/power/suspend-and-interrupts.txt
> @@ -112,8 +112,9 @@ any special interrupt handling logic for it to work.
>  IRQF_NO_SUSPEND and enable_irq_wake()
>  -------------------------------------
>  
> -There are no valid reasons to use both enable_irq_wake() and the IRQF_NO_SUSPEND
> -flag on the same IRQ.
> +There are very few valid reasons to use both enable_irq_wake() and the
> +IRQF_NO_SUSPEND flag on the same IRQ, and it is never valid to use both for the
> +same device.
>  
>  First of all, if the IRQ is not shared, the rules for handling IRQF_NO_SUSPEND
>  interrupts (interrupt handlers are invoked after suspend_device_irqs()) are
> @@ -122,4 +123,13 @@ handlers are not invoked after suspend_device_irqs()).
>  
>  Second, both enable_irq_wake() and IRQF_NO_SUSPEND apply to entire IRQs and not
>  to individual interrupt handlers, so sharing an IRQ between a system wakeup
> -interrupt source and an IRQF_NO_SUSPEND interrupt source does not make sense.
> +interrupt source and an IRQF_NO_SUSPEND interrupt source does not generally
> +make sense.
> +
> +In rare cases an IRQ can be shared between a wakeup device driver and an
> +IRQF_NO_SUSPEND user. In order for this to be safe, the wakeup device driver
> +must be able to discern spurious IRQs from genuine wakeup events (signalling
> +the latter to the core with pm_system_wakeup()), must use enable_irq_wake() to
> +ensure that the IRQ will function as a wakeup source, and must request the IRQ
> +with IRQF_COND_SUSPEND to tell the core that it meets these requirements. If
> +these requirements are not met, it is not valid to use IRQF_COND_SUSPEND.
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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