Messages in this thread | | | Subject | Re: [PATCH 4/5] Centralise NO_IRQ definition | From | Benjamin Herrenschmidt <> | Date | Tue, 22 Nov 2005 08:16:15 +1100 |
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> The fact is, 0 _is_ special. Not just for hardware, but because 0 has a > magical meaning as "false" in the C language.
I don't agree, irq 0 has been a valid irq on a number of platforms for ages (including your own G5, at least some of them have the SATA irq at 0 :) and this didn't cause any problem for most drivers. The few ones that have done broken assumption have been easily fixed using NO_IRQ.
"Translating" it means some ugly translation work all over the place, which means overhead in the interrupt path (ok, not that much but still), plus finding some magic number to put 0 on, which makes things much more complicated for archs that have interrupts sorted in nice blocks of power of two, etc... a significant burden on arch/PIC code for no good reason imho.
I hate arbitrary "translations" when they aren't strictly necessary. It's common to have a constant for a "not valid" number in spaces where "0" is a valid value, I don't think that "looking simpler" to dump driver writers is worth it in this case.
Ben.
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