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Subject: Re: [PATCH 4/5] Centralise NO_IRQ definition
From: David Woodhouse <dwmw2@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@osdl.org>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
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Date: Tue, 22 Nov 2005 19:03:33 +0000
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On Tue, 2005-11-22 at 18:37 +0000, David Howells wrote:
> 
>  (3) Having to translate a cookie for a specific IRQ means that the IRQ
>      handling code will be slower and more complex, or is going to avoid the
>      issue and be naughty and not deal with irq == NO_IRQ properly:
> 
>      The x86 PIC reports it as IRQ 0 having happened. In which case, by your
>      argument, you _have_ to translate it: you're not allowed to pass NO_IRQ to
>      setup_irq(), and you're not allowed to pass it to the interrupt handler -
>      in this case timer_interrupt(). Doing otherwise is wrong, insane, etc...

This is true. If we're suddenly going to start pretending that IRQ 0
isn't a valid interrupt merely on the basis that "x86 doesn't use it"¹,
then we can't really go making an exception to allow us to use IRQ 0 on
i386.

-- 
dwmw2
¹ ...despite the fact that even that isn't true on legacy-free machines.