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Date: Sat, 15 Aug 2009 11:55:03 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Pavel Machek <pavel@ucw.cz>,
       LKML <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Peter Zijlstra <peterz@infradead.org>,
       Dmitry Torokhov <dmitry.torokhov@gmail.com>,
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       Joonyoung Shim <jy0922.shim@samsung.com>, m.szyprowski@samsung.com,
       t.fujak@samsung.com, kyungmin.park@samsung.com,
       David Brownell <david-b@pacbell.net>, Daniel Ribeiro <drwyrm@gmail.com>,
       arve@android.com, Barry Song <21cnbao@gmail.com>
Subject: Re: [RFC patch 2/3] genirq: Add buslock support for irq chips on
	slow busses
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* Mark Brown <broonie@opensource.wolfsonmicro.com> wrote:

> On Fri, Aug 14, 2009 at 12:20:49PM +0200, Thomas Gleixner wrote:
> > On Fri, 14 Aug 2009, Pavel Machek wrote:
> 
> > > AFAICT this means that driver would need to know what kind of IRQ it
> > > is hooked to, right? That will lead to some ugly code in drivers that
> > > can handle both normal and slowbus irqs, right?
> 
> > Are there such drivers in reality ?
> 
> Yes.  The GPIO based stuff is the prime example but there's other 
> examples - one is the WM831x touchscreen (no driver in mainline 
> yet) which can use interrupts via the main interrupt controller on 
> the CPU but also has the option of bringing the interrupt signals 
> out to dedicated pins on the chip for direct connection to the CPU 
> precisely to avoid the overheads of these slow interrupt 
> controllers.

This would call for Thomas's first version of the patch, that is 
transparent to drivers - the IRQ subsystem will know how to lock 
access to the line.

How about implementing that first patch in a cleaner way - can we 
somehow express the slow-bus property purely via the irqchip? Or is 
that too lowlevel?

	Ingo