linux-kernel - Re: Seeking clarity on IRQCHIP_MASK_ON

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Date:	Mon, 10 Sep 2012 16:26:45 +0530
From:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	NeilBrown <neilb@...e.de>, "Rafael J. Wysocki" <rjw@...k.pl>,
	lkml <linux-kernel@...r.kernel.org>, linux-omap@...r.kernel.org,
	Kevin Hilman <khilman@...prootsystems.com>
Subject: Re: Seeking clarity on IRQCHIP_MASK_ON_SUSPEND

Thomas,

On Mon, Sep 10, 2012 at 3:58 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Mon, 10 Sep 2012, NeilBrown wrote:
>>
>> The IRQCHIP_MASK_ON_SUSPEND flag seems to be hard to use correctly, so either
>> I'm understanding it wrongly, or it could be made easier to use.
>> If the first case, I'm hoping that some improvement to documentation might
>> result.  If the second, then maybe we can fix the code.
> ...
>> Is anyone able to give a definitive answer on this?  Should
>> IRQCHIP_MASK_ON_SUSPEND be removed?
>
> The whole point of IRQCHIP_MASK_ON_SUSPEND is to deal with hardware
> designed by geniuses.
>
> Most SoCs have a way to mark the interrupts which serve as a wake up
> source as such. All other interrupts are magically "masked" on entry
> to suspend.
>
Just to support this, IRQCHIP_MASK_ON_SUSPEND does work with quite
a few ARM platforms too. OMAP already uses it in mainline and I have
seen patches for U500 and Tegra SOCs. Most of these usages are with
IRQ chips who doesn't have any driver run time PM supported and
the IRQ CHIP itself is shutdown when the CPU/CPU cluster gets
power down. So as far as functionality concerned with the flag,
it does what it suppose to do.

> Now there is hardware which is missing such a control, so we need to
> mask the non wakeup interrupts right before going into suspend.
>
> That's what IRQCHIP_MASK_ON_SUSPEND does. Not more, not less. See
> commit d209a699a0b for more ugly details.
>
> You might be looking for a different functionality. Can you explain
> what you need?
>
Neil's email came from a discussion on the usage of this flag for
OMAP GPIO irqchip which I proposed. With the flag, when the
lazy check_irq routine is called, the GPIO driver is runtime suspended
and hence the late mask/unmask calls take abort(clocks are already gated).
GPIO IRQCHIP is secondary IRQCHIP connected to 1 interrupt line
per bank(32 GPIOs) to the primary interrupt controller IRQCHIP.

Hope this gives bit more clarity to the discussed problem.

Regards
Santosh
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