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

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Date:	Mon, 5 Dec 2011 16:11:57 +0000
From:	Dave Martin <dave.martin@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	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 Sat, Dec 03, 2011 at 10:12:53AM +1100, Benjamin Herrenschmidt wrote:
> On Fri, 2011-12-02 at 11:28 -0800, Linus Torvalds wrote:
> > On Fri, Dec 2, 2011 at 11:26 AM, Dave Martin <dave.martin@...aro.org> wrote:
> > >
> > > This is now broken on ARM where, for good or bad, NO_IRQ currently is
> > > used and is -1.
> > >
> > > How do we resolve it?  If we are ready to eliminate NO_IRQ from
> > > drivers/of/irq.c (or indeed, all code that uses it) and just use 0 for
> > > that case, we should surely just do it... but I'm not confident I can
> > > judge on that.
> > 
> > Just stop using NO_IRQ. First in drivers/of/irq.c, then in any drivers
> > as you notice breakage.
> 
> Agreed. In fact the whole hack in drivers/of/irq.c was to accomodate ARM
> which still uses -1, powerpc changed to 0 a long time ago.
> 
> Now that we have a generic remapper between HW and "linux" IRQ numbers,
> there is no reason to stick to -1 even on ARM.
> 
> > 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.

I worry that if we just change the convention for the OF case, we'll end
up with OF-ised platform drivers which have to deal with a different no-
irq convention depending on whether they are probed as platform drivers
or through the OF framework ... and these ported or semi-ported drivers
will be intermixed with unported drivers, confusing maintainers.
 
If board code starts initialising platform data for non-OF-ised platform
drivers based on IRQ numbers fetched via the OF code, things will get
even more confused...

Cheers
---Dave

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