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Date: Tue, 22 Nov 2005 07:04:25 -0700
From: Matthew Wilcox <matthew@wil.cx>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: David Woodhouse <dwmw2@infradead.org>, Paul Mackerras <paulus@samba.org>,
       Ingo Molnar <mingo@elte.hu>, Linus Torvalds <torvalds@osdl.org>,
       David Howells <dhowells@redhat.com>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org, Russell King <rmk@arm.linux.org.uk>,
       Ian Molton <spyro@f2s.com>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH 4/5] Centralise NO_IRQ definition
Message-ID: <20051122140425.GK1598@parisc-linux.org>
References: <Pine.LNX.4.64.0511211047260.13959@g5.osdl.org> <20051121190632.GG1598@parisc-linux.org> <Pine.LNX.4.64.0511211124190.13959@g5.osdl.org> <20051121194348.GH1598@parisc-linux.org> <Pine.LNX.4.64.0511211150040.13959@g5.osdl.org> <20051121211544.GA4924@elte.hu> <17282.15177.804471.298409@cargo.ozlabs.ibm.com> <1132611631.11842.83.camel@localhost.localdomain> <1132657991.15117.76.camel@baythorne.infradead.org> <1132668939.20233.47.camel@localhost.localdomain>
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On Tue, Nov 22, 2005 at 02:15:39PM +0000, Alan Cox wrote:
> On Maw, 2005-11-22 at 11:13 +0000, David Woodhouse wrote:
> > Yes, there are drivers which are currently broken and assume irq 0 is
> > 'no irq'. They are broken. Let's just fix them and not continue the
> > brain-damage.
> 
> 0 in the Linux kernel has always meant 'no IRQ' and it makes it natural
> to express in C (and on some cpus more efficient too).
> 
> What if my hardware has an IRQ -1 ;)

Then it falls off the bottom of the irq_desc array.  Already tried that,
hence patch 1/5.

That was a great one to debug, btw.  "The machine hangs when I select
processor type PA8000 but works with processor type PA7200".  Why?
synchronize_irq() spins waiting for a bit to become clear ... for some
reason that bit was always set with PA8000 and always clear with PA7200.
http://lists.parisc-linux.org/pipermail/parisc-linux/2005-October/027485.html