linux-kernel - Re: [PATCH] ata: Don't use NO_IRQ in pata_of

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Message-ID: <alpine.LFD.2.02.1112051310150.2357@xanadu.home>
Date:	Mon, 5 Dec 2011 13:18:30 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Dave Martin <dave.martin@...aro.org>
cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Anton Vorontsov <cbouatmailru@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	devicetree-discuss@...ts.ozlabs.org,
	LKML <linux-kernel@...r.kernel.org>, linux-ide@...r.kernel.org,
	Randy Dunlap <rdunlap@...otime.net>,
	linux-next@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Jeff Garzik <jgarzik@...hat.com>,
	Pawel Moll <pawel.moll@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ata: Don't use NO_IRQ in pata_of_platform driver

On Mon, 5 Dec 2011, Dave Martin wrote:

> On Mon, Dec 05, 2011 at 12:40:16PM -0500, Nicolas Pitre wrote:
> > On Mon, 5 Dec 2011, Dave Martin wrote:
> > > On Sat, Dec 03, 2011 at 10:12:53AM +1100, Benjamin Herrenschmidt wrote:
> > > > On Fri, 2011-12-02 at 11:28 -0800, Linus Torvalds wrote:
> > > > > Don't *change* NO_IRQ to zero (that whole #define is broken - leave it
> > > > > around as a marker of brokenness), just start removing it from all the
> > > > > ARM drivers that use the OF infrastructure. Which is presumably not
> > > > > all that many yet.
> > > > > 
> > > > > So whenever you find breakage, the fix now is to just remove NO_IRQ
> > > > > tests, and replace them with "!irq".
> > > > 
> > > 
> > > Russell, do you know whether it would make sense to set a timeline for 
> > > removing NO_IRQ from ARM platforms and migrating to 0 for the no-interrupt
> > > case?  I'm assuming that this mainly involves migrating existing hard-wired
> > > code that deals with interrupt numbers to use irq domains.
> > 
> > How many drivers do use IRQ #0 to start with?  We might discover that in 
> > practice there is only a very few cases where this is an issue if 0 
> > would mean no IRQ.
> 
> The total number of files referring to NO_IRQ is not that huge:
> 
> arch/arm/	188 matches in 39 files
> drivers/	174 matches in 84 files
> 
> Unfortunately, NO_IRQ is often not spelled "NO_IRQ".  It looks like the assumption
> "irq < 0 === no irq" may be quite a lot more widespread than "NO_IRQ === no irq".
> Since there's no specific thing we can grep for (and simply due to volume)
> finding all such instances may be quite a bit harder.
[...]

ARgh.

My point was about current actual usage of the IRQ numbered 0 which 
probably prompted the introduction of NO_IRQ in the first place.  What I 
was saying is that the number of occurrences where IRQ #0 is currently 
used into drivers that would get confused if 0 would mean no IRQ is 
probably quite small.

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.


Nicolas
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