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SubjectRe: 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?

--

Doug Ledford <dledford@dialnet.net>
Opinions expressed are my own, but
they should be everybody's.

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