On Thu, Oct 25, 2007 at 03:57:01PM +0100, Maciej W. Rozycki wrote:
> > That said, irq 0 is imho totally valid (take the good old PIT timer
> > interrupt of the PC as the classic example) and treating it as an invalid
> > interrupt number is broken.
>
> I would rather -1 stood for the invalid IRQ number -- unlike with 0
> chances are nobody will need 4G of interrupt lines or vectors (as
> applicable) in a single system. We sort of escape the problem with the
> MIPS processors because the IP0 bit of the Cause register is a software
> interrupt that is not used by devices, but still some platforms bypass the
> built-in interrupt "controller" as only a single source is used in the
> Cause register and want to start the numbering of lines in the external
> controller from 0.
Time to convert those platforms to irq_cpu.c as well.
Anyway, I recall there was an argument against using -1 as the invalid
irq number - but since -1 is not a valid index into the irq_desc array
for example I would consider such use broken. But does anybody recall
the details?
Ralf
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