Re: [PATCH 4/5] Centralise NO_IRQ definition

From: Ingo Molnar
Date: Mon Nov 21 2005 - 16:15:34 EST

* Linus Torvalds <torvalds@xxxxxxxx> 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.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at