Re: Bugfixes: PCI devices get assigned redundant IRQs

[H. Peter Anvin]

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.

	-hpa
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