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

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Date:	Wed, 6 Jul 2016 16:49:04 +0000
From:	Jason Cooper <jason@...edaemon.net>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	Sebastian Frias <sf84@...oste.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 Wed, Jul 06, 2016 at 11:30:48AM +0200, Thomas Gleixner wrote:
> On Wed, 6 Jul 2016, Marc Zyngier wrote:
> > On 05/07/16 20:24, Thomas Gleixner wrote:
> > > On Tue, 5 Jul 2016, Marc Zyngier wrote:
> > >> 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.
> 
> That's not necessarily Linux specific. The problem arises with any other OS as
> well.

I could see a property

	irq,no-mux = <3 7 13 19 23 ...>;

Or "irq,fastpath".  It's describing an optimal configuration of the
system.  $driver for $OS can route those first individually.  The others
would be eligible for muxing.

thx,

Jason.