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Message-ID: <20111206110554.53bddd14@lxorguk.ukuu.org.uk>
Date: Tue, 6 Dec 2011 11:05:54 +0000
From: Alan Cox <alan@...rguk.ukuu.org.uk>
To: Russell King - ARM Linux <linux@....linux.org.uk>
Cc: Dave Martin <dave.martin@...aro.org>,
Nicolas Pitre <nicolas.pitre@...aro.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Anton Vorontsov <cbouatmailru@...il.com>,
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
> Even better. Avoid the first 16 IRQ numbers altogether - so that ISA
> drivers which have these numbers hard-encoded in them will see failures
> if they're expecting standard ISA IRQ numbering.
The ISA bus space is non-discoverable so that doesn't make any sense.
> But.. let's make one thing clear: Alan Cox and Linus have been going on
> about how IRQ0 should not be used. Let's be crystal clear: even x86
> uses IRQ0. It happens to be the PIC timer, and that gets claimed early
> on during the x86 boot. So please don't tell me that x86 avoids IRQ0.
> It doesn't. It just happens that x86 never shows IRQ0 to anything but
> the i8253 PIC driver.
x86 has an internal invisible IRQ 0 on some platforms. It's never exposed
beyond the arch code.
> So lets see how x86 squeels if we make the i8253 PIC driver reject IRQ0.
> I bet that there'd be absolute fury at such a suggestion.
Actually it would be about ten minutes work to remap it to some other
number that isn't used. It never goes via request_irq or via any core or
driver layer code however.
In the ARM case the same is going to be true. If you have IRQ 0 plumbing
that only goes internally in the arch/arm code - eg an ARM with IRQ 0
wired to something totally arch specific and non-driver then it's not
going to break and like the internals of x86 doesn't matter.
> When x86 sorts this out, there _might_ be some more motivation to take
> such comments seriously. Until then it's more like a joke.
Pity you feel that way, but if ARM wants to continue to break more and
more as we clean up NO_IRQ for everything else that's your privilege, but
don't expect any sympathy.
Alan
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