Date: Tue, 19 Apr 2011 18:09:19 -0500
From: Scott Wood <scottwood@freescale.com>
To: "Hans J. Koch" <hjk@hansjkoch.de>
CC: Grant Likely <grant.likely@secretlab.ca>,
        <devicetree-discuss@lists.ozlabs.org>, <linux-kernel@vger.kernel.org>,
        <john.williams@petalogix.com>
Subject: Re: [PATCH v3] uio/pdrv_genirq: Add OF support
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	<20110419060816.GA5252@ponder.secretlab.ca>
	<20110419220018.GB2772@local>
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On Wed, 20 Apr 2011 00:00:18 +0200
"Hans J. Koch" <hjk@hansjkoch.de> wrote:

> On Tue, Apr 19, 2011 at 12:08:16AM -0600, Grant Likely wrote:
> > PowerPC and x86 will return 0 for an unassigned IRQ, as will most platforms.
> 
> That might be right for these architectures. On ARM SoCs, IRQ0 is often a
> normal irq like any other (e.g. "Audio DMA Controller 1" on Telechips TCC8000).

It's true on at least some powerpc and x86 interrupt controllers as well.
ARM isn't special. :-)

I'm not sure what goes on on x86, as I see a real " 0:" in
/proc/interrupts.  But on powerpc, Linux's IRQ numberspace is decoupled
from that of any IRQ controller.  This is mainly to accommodate multiple
IRQ controllers with their own numberspaces in the same system; being able
to avoid irq 0 is just a bonus.

-Scott

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