linux-kernel - Re: [patch 3/4] genirq: add a quick check handler

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Message-ID: <alpine.LFD.2.00.0902270008410.9135@localhost.localdomain>
Date:	Fri, 27 Feb 2009 00:11:06 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, peterz@...radead.org,
	arjan@...radead.org, rostedt@...dmis.org, jonathan@...masters.org
Subject: Re: [patch 3/4] genirq: add a quick check handler

On Thu, 26 Feb 2009, Andrew Morton wrote:
> >  enum irqreturn {
> >  	IRQ_NONE,
> >  	IRQ_HANDLED,
> > +	IRQ_NEEDS_HANDLING,
> >  };
> 
> The enquiring mind is wondering which of these values the quickcheck
> handler can return.  IRQ_NEEDS_HANDLING or IRQ_NONE?  Or can it
> legitimately return IRQ_HANDLED?  If so, what would that semantically
> mean?

Yes it can return IRQ_HANDLED as well. That means no further action
(calling the slow path handler) is needed.
 
> I mean, an IRQ handler could easily have a super-fast-path and a slow
> path.  It could decide to do the super-fast operation in hard irq
> context and return IRQ_HANDLED, and return IRQ_NEEDS_HANDLING if
> slow-path handling is needed?
> 
> It's all a bit unclear and deserves documenting and thinking about.

Yep, I need to sit down and write up documentation.
 
> > + *      @quick_check_handler: Function called before the real interrupt
> > + *			handler. It checks if the interrupt originated
> > + *			from the device. This can be NULL.
> 
> So what semantics are implemented if this pointer is NULL?  We just
> assume IRQ_NEEDS_HANDLING?

Correct.

	tglx
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