From mboxrd@z Thu Jan  1 00:00:00 1970
From: James Bottomley <James.Bottomley@HansenPartnership.com>
Subject: Re: [PATCH] ata: Don't use NO_IRQ in pata_of_platform driver
Date: Mon, 05 Dec 2011 13:19:14 -0600
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>, Dave Martin <dave.martin@linaro.org>, Russell King - ARM Linux <linux@arm.linux.org.uk>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Linus Torvalds <torvalds@linux-foundation.org>, Anton Vorontsov <cbouatmailru@gmail.com>, Stephen Rothwell <sfr@canb.auug.org.au>, Andrew Morton <akpm@linux-foundation.org>, devicetree-discuss@lists.ozlabs.org, LKML <linux-kernel@vger.kernel.org>, linux-ide@vger.kernel.org, Randy Dunlap <rdunlap@xenotime.net>, linux-next@vger.kernel.org, Ingo Molnar <mingo@elte.hu>, Jeff Garzik <jgarzik@redhat.com>, Pawel Moll <pawel.moll@arm.com>, linux-arm-kernel@lists.infradead.org
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On Mon, 2011-12-05 at 18:45 +0000, Alan Cox wrote:
> > But as you illustrated, there is a large number of drivers that already 
> > assume no IRQ is < 0, even if they don't use any IRQ #0 themselves.  
> > That is a much bigger problem to fix.
> 
> And a much larger number assuming the reverse is true which are hiding
> potential bugs on ARM.
> 
> Looking at the serial stuff the best checks appear to be looking at
> "irq", "-1" and NO_IRQ.
> 
> For migration stuff that's doing broken things like
> 
> 	if (irq < 0)
> 
> can be changed to
> 
> 	if (irq <= 0)
> 
> and that can be done before NO_IRQ itself is nailed on ARM and PA-RISC.

To be honest, we don't care very much.  Parisc interrupts are cascading
and mostly software assigned (except our EIEM which we keep internal).
We use a base offset at 16 or 64 (depending on GSC presence or not) so
IRQs 0-15 aren't legal on parisc either (we frob some of the hard coded
ISA interrupts on the WAX eisa bus).

We use NO_IRQ as an IRQ assignment error return and that's about it (and
that error shouldn't ever really occur).

James