On my machine, the PCI BIOS remembers the IRQ it has assigned to a card
in the system. If I go and re-arrange the cards, they still have the same
IRQ's they were assigned before I did that.
There is a system BIOS setting called "enable rewrite". When I select
this, it will re-scan the cards and re-allocate the IRQ's on the next
reboot, then disable it again automatically. I had to use this when I've
added ISA PNP cards that sorta wanted to conflict with the PCI cards
automatically for some reason.
Don't ask me, I didn't design the thing to do whatever it does :)
Brian
On Tue, 21 Apr 1998, Colin Coe wrote:
> I am no expert, however, I believe that the first PCI device found by the
> BIOS is *always* IRQ 9, the second PCI device IRQ is dependant on whether
> IRQ 10 is being used by an ISA or EISA device.
>
> This is from my limited understanding...
>
> CC
>
> -----Original Message-----
> From: Doug Ledford <dledford@dialnet.net>
> To: Neal Becker <neal@ctd.comsat.com>
> Cc: linux-kernel@vger.rutgers.edu <linux-kernel@vger.rutgers.edu>
> Date: Tuesday, 21 April 1998 20:52
> Subject: Re: something strange - is it p2x4?
>
>
> >Neal Becker wrote:
> >>
> >> I have an Intel AL440LX board. I have an AHA2940UW pci card. No
> >> matter what slot I plug the AHA2940 into, /proc/pci says it's INT9.
> >>
> >> The Intel doc on the AL440LX board says that the interrupt line will
> >> vary with the slot, from INTA - INTD. It says the p2x4 PCI/ISA chip
> >> will map INTA-INTD to various interrupts. I have NO interrupts
> >> reserved for ISA. I have NO other PCI cards. I have one AGP video
> >> card, which also reports it's on INT9 (which is the reason I have a
> >> problem).
> >>
> >> What sets up the mapping of PCI interrupts to INT1-15? I understand
> >> it's handled by the P2X4 chip. Is this strictly a bios function, or
> >> does the linux P2X4 driver set this up?
> >>
> >> Stranger still, if I stop the boot process when prompted by the
> >> AHA2940 bios and view the config, it claims it's using INT11. Did
> >> linux change it when it booted? Is /proc/pci lying?
> >>
> >> This is 2.1.96 BTW.
> >
> >Actually, from what I can tell so far, this isn't an isolated case. It
> >appears to be related to the switch over from pcibios_* function usage to
> >the newer pci_* functions. In the past, we could reliably read the irq
> >value for the card from the pcibios config space by reading the
> >PCI_CONFIG_IRQLINE area (I think that's the right mnemonic). Now, in
> 2.1.96
> >and above, we instead get the irq value from the pdev->irq structure value.
> >If that value isn't right (and it appears to not be right on certain
> >machines, such as this) then we don't get any interrupts and the system
> ends
> >up hanging, or going into a timeout/reset loop. I would guess that the
> >actual PCI BIOS areas and the PCI CONFIG areas are disagreeing on what the
> >IRQ is, and that's causing the problem, but I'm not a PCI expert, so I
> would
> >defer the actual determination to Martin Mares. Any comments on this
> >Martin?
>
>
>
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