Messages in this thread | | | Date | Sun, 28 Jan 2007 00:04:41 -0800 | From | "H. Peter Anvin" <> | Subject | Re: Bugfixes: PCI devices get assigned redundant IRQs |
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Andreas Block wrote: >> >> Aren't there platforms for which irq = 0 is a valid irq ? > > As far as I understand the PCI spec, the answer to your question seems > to be: no > (or I'm missing something). > > Don't get me wrong. I'm not talking about system IRQs, but about the > value of the Interrupt Pin Register in PCI configuration space. > > The PCI Local Bus Specification in Revision 3.0 from 3rd February 2004 > says on page 223 about the content of Interrupt Pin register: > > Value 0x00: _No_ interrupt > Values 0x01 to 0x04: Interrupt lines A to D > And values 5 to 0xFF are reserved. > > So I'd say, the "correction" of greater values than four to a value of > one seems discussable, too. Because it will break any future changes of > the PCI spec. >
I think you're confusing the Interrupt Line register and the Interrupt Pin register. The Interrupt Line register is platform-dependent, but on x86 platforms it generally contains the IRQ number (and IRQ 0 is valid, although in practice it is never used since IRQ 0 is the system timer and is never connected to the PCI bus), or 255 meaning "none" -- see the footnote on page 223 of the PCI 3.0 spec.
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