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SubjectRe: [PATCH 4/5] Centralise NO_IRQ definition

* Linus Torvalds <torvalds@osdl.org> wrote:

> At which point you might as well just do something like
>
> struct interrupt_descriptor {
> unsigned int nr:31;
> unsigned int valid:1;
> };
>
> and then people can just say
>
> if (!dev->irq.valid)
> return;
>
> instead, which is also readable, and where you simply cannot do the old
> "if (!dev->irq)" at all.
>
> The fact is, 0 _is_ special. Not just for hardware, but because 0 has
> a magical meaning as "false" in the C language.

yeah, i wanted to suggest this originally, but got distracted by the x86
quirk that 'IRQ#0' is often the i8253 timer interrupt.

is there any architecture where irq 0 is a legitimate setting that could
occur in drivers, and which would make NO_IRQ define of 0 non-practical?
If not (which i think is the case) then we should indeed standardize on
0. (in one way or another) It's not like any real driver will ever have
IRQ#0 even on a PC: the timer IRQ is 'known' to be routed to 0, and we
do a platform-specific setup_irq() on it. Not a good reason to abstract
the notion of 'no irq' away into a define.

in fact we dont even have to do the irq.valid thing, !dev->irq is
obviously readable.

Ingo
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