linux-kernel - Re: [patch] x86 supports NO

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Date:	Mon, 23 Jun 2008 15:20:45 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	David Brownell <david-b@...bell.net>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, hpa@...or.com
Subject: Re: [patch] x86 supports NO_IRQ convention

On Mon, 23 Jun 2008 04:29:36 -0700
David Brownell <david-b@...bell.net> wrote:

> On Monday 23 June 2008, Alan Cox wrote:
> > Zero is not a valid IRQ in the kernel mapping of things.
> 
> That's counter-factual:

There are historical reasons for the timer tick (which isn't visible
outside arch code) being 0 on x86.

> I certainly agree it'd be convenient to be able to just test
> for IRQ being nonzero. 

0 means "no IRQ" in things like dev->irq. Lots of driver code assumes
this and it has been decreed 'correct'.

Alan
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