Date:	Mon, 5 Dec 2011 18:02:53 +0000
From:	Dave Martin <dave.martin@...aro.org>
To:	Nicolas Pitre <nicolas.pitre@...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, 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.

For example, git grep 'irq.*\(>=\|<[^=]\) *0' gives

drivers/	435 matches in 314 files
arch/arm/	18 matches in 15 files

A few examples:
drivers/input/mouse/pxa930_trkball.c:   if (irq < 0) {
drivers/input/keyboard/tegra-kbc.c:     if (irq < 0) {
drivers/crypto/omap-sham.c:     if (dd->irq >= 0)

...etc., etc., although there are probably a fair number of false positives here.


whereas git grep 'irq.*\(<\|>\|<=\|>=\|==\|!=\) \+-1' gives

drivers/	68 matches in 28 files
arch/arm/	18 matches in 15 files

Examples: 


...and that's just the code which is C and is also kind enough to put
irq numbers in variables with names containing "irq".

It also doesn't catch people initialising variables or struct/array
members to -1, unadorned "-1" arguments to functions and so on... though
those are likely to appear in mostly the same files matching the above
expressions, it won't be an exact 1:1 correspondence.


Cheers
---Dave
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