linux-kernel - Re: [RFC patch 2/3] genirq: Add buslock support for irq chips on slow busses

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Message-ID: <20090815095503.GB15831@elte.hu>
Date:	Sat, 15 Aug 2009 11:55:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Pavel Machek <pavel@....cz>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Trilok Soni <soni.trilok@...il.com>,
	Brian Swetland <swetland@...gle.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	m.szyprowski@...sung.com, t.fujak@...sung.com,
	kyungmin.park@...sung.com, David Brownell <david-b@...bell.net>,
	Daniel Ribeiro <drwyrm@...il.com>, arve@...roid.com,
	Barry Song <21cnbao@...il.com>
Subject: Re: [RFC patch 2/3] genirq: Add buslock support for irq chips on
	slow busses


* Mark Brown <broonie@...nsource.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
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