linux-kernel - Re: [RFC PATCH v1] irqchip: add support for SMP irq router

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Date:	Wed, 6 Jul 2016 09:58:38 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Sebastian Frias <sf84@...oste.net>,
	Jason Cooper <jason@...edaemon.net>, Mason <slash.tmp@...e.fr>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v1] irqchip: add support for SMP irq router

On 05/07/16 20:24, Thomas Gleixner wrote:
> On Tue, 5 Jul 2016, Marc Zyngier wrote:
>> On 05/07/16 17:59, Sebastian Frias wrote:
>>> Well, if you the domains should not be described in the DT and that they should
>>> be somehow hardcoded into the drivers' code, it should not be hard indeed.
>>
>> Hardcoded? No way. You simply implement a route allocator in your
>> driver, assigning them as needed. And yes, if you have more than 24
>> interrupts, they get muxed.
> 
> There is one caveat though. Under some circumstances (think RT) you want to
> configure which interrupts get muxed and which not. We really should have that
> option, but yes for anything which has less than 24 autorouting is the way to
> go.

Good point. I can see two possibilities for that:

- either we describe this DT with some form of hint, indicating what are
the inputs that can be muxed to a single output. Easy, but the DT guys
are going to throw rocks at me for being Linux-specific.

- or we have a way to express QoS in the irq subsystem, and a driver can
request an interrupt with a "make it fast" flag. Of course, everybody
and his dog are going to ask for it, and we're back to square one.

Do we have a way to detect which interrupt is more likely to be
sensitive to muxing? My hunch is that if it is requested with
IRQF_SHARED, then it is effectively muxable. Thoughts?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...