On Tue, Dec 06, 2011 at 11:05:54AM +0000, Alan Cox wrote: > > Even better. Avoid the first 16 IRQ numbers altogether - so that ISA > > drivers which have these numbers hard-encoded in them will see failures > > if they're expecting standard ISA IRQ numbering. > > The ISA bus space is non-discoverable so that doesn't make any sense. > > > But.. let's make one thing clear: Alan Cox and Linus have been going on > > about how IRQ0 should not be used. Let's be crystal clear: even x86 > > uses IRQ0. It happens to be the PIC timer, and that gets claimed early > > on during the x86 boot. So please don't tell me that x86 avoids IRQ0. > > It doesn't. It just happens that x86 never shows IRQ0 to anything but > > the i8253 PIC driver. > > x86 has an internal invisible IRQ 0 on some platforms. It's never exposed > beyond the arch code. > > > So lets see how x86 squeels if we make the i8253 PIC driver reject IRQ0. > > I bet that there'd be absolute fury at such a suggestion. > > Actually it would be about ten minutes work to remap it to some other > number that isn't used. It never goes via request_irq or via any core or > driver layer code however. > > In the ARM case the same is going to be true. If you have IRQ 0 plumbing > that only goes internally in the arch/arm code - eg an ARM with IRQ 0 > wired to something totally arch specific and non-driver then it's not > going to break and like the internals of x86 doesn't matter. > > > When x86 sorts this out, there _might_ be some more motivation to take > > such comments seriously. Until then it's more like a joke. > > Pity you feel that way, but if ARM wants to continue to break more and > more as we clean up NO_IRQ for everything else that's your privilege, but > don't expect any sympathy. For the platforms I care about, it probably won't break. For those which do break, it's a matter of fixing their include/mach/irqs.h and the code in their irqchips to convert the IRQ number to the correct bitmask for the register. However, I have suggested in the past that new platforms _should_ avoid not just IRQ0 but IRQ0-15 (for a completely different reason to that of 'IRQ0 means no IRQ'.) But such comments just get ignored, so I just don't see the point in doing anything about this. If people experience breakage, so be it. I too will have little sympathy but not for the same reason. -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
