It could be some bug in your 3w-9xxx driver.
Nope. e1000 does the same thing in that slot; "nobody cared" immediately on driver load. Definately not unique to the 3w-9xxx driver.
I noticed that Irq 26 is used by card on slot 4 (8131 a) Irq 25 is used by card on slot 3 (8131 a) Irq 30 is used by card on slot 2 (8131 b) Slot 1: is HTX
Ahh. Closer inspection of the mobo artwork reveals that there are two sockets on the B-bus and one on the A labelled (in order: HTX, PCIX2, PCI64_1, PCI64_2). I thought there were two on the A and one on the B (well, that's how _I_ would have built it... ;-)).
So the problem isn't a B-bus problem it's a B-bus 2nd slot (slot 4) problem. I think your 'a' and 'b' in the quoted text above are backwards from reality (or at least from the board artwork).
This means it's a non-issue for me practically; I can get away with never plugging anything into slot 4, like ever. But if it _is_ an LB problem, it'd be nice to get it licked so the board can be declared 'working'. :)
Might there be some mystery hardware that I just don't know about that's initted by LB/etherboot+filo, still running, and sharing the IRQ with slot 4? Does linux generate 'nobody cared' for IRQs with zero drivers attached or does it silently drop them?
Thanks again,
-mcq