linux-kernel - Re: SOC-specific action for irq_set

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Date:	Wed, 20 Jul 2016 06:23:33 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Michal Simek <michal.simek@...inx.com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: SOC-specific action for irq_set_wake

Hi Thomas,

On Wed, 2016-07-20 at 08:28:35 +0200, Thomas Gleixner wrote:
> On Tue, 19 Jul 2016, Sören Brinkmann wrote:
> > we are working on the PM solution for Zynq MPSOC and ran into some
> > problem when setting the wake source.
> > 
> > The situation is that when the A53 is in suspend, the GIC(v2) may be
> > powered down. In that state a companion core is handling wake
> > events/IRQs, but we expect the OS/Linux to notify the companion core
> > about what device/IRQ is a wake up source. Hence, my idea was to capture
> > enabling/disabling wake IRQs in our platform PM code and then
> > communicate with the FW as needed during suspend operations. The problem
> > is: I don't see a good way to notify the platform code about these
> > events.
> > 
> > My ideas were:
> > 1. Use the irq_chip irq_set_wake function
> >   My thought was to implement the irq_set_wake function in a
> >   SOC-specific way (could even be generic and call some notifier chain or
> 
> Don't even think about notifier chains.
> 
> >   similar) to notify the platform PM code when a device/IRQ is
> >   enabled/disabled as wake up source.
> >   My problem is that the SKIP_IRQ_SET_WAKE flag is set in the generic
> >   driver (drivers/irqchip/irq-gic.c) and platforms cannot implement
> >   irq_set_wake without changes in the common code.
> 
> So and because it requires changes in the common code you think aboiut
> notifiers and other absurdities. Come on, common code is not a sacred cow. It
> can be modified and if you need for your particular platform that
> SKIP_IRQ_SET_WAKE is cleared, then there are a gazillion of sane ways to do
> that.

I'm not afraid of changing it, but I was hoping to get an idea of what
an acceptable solution would look like, as I don't want to run of into
any of the directions that are not sane and have it shoot down in the
end (like my notifier approach apparently would). I remembered the mentioned
extensions mechanism which disappeared. Hence, I thought it might be a
better idea to check beforehand why and what happened and what
alternative approach may be an acceptable solution for that problem.

	Thanks,
	Sören