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
