The p-Code Machine

A while back a friend had a problem with his HP Mini netbook, which has a Marvell Yukon 2 Fast Ethernet NIC. When the netbook was booted without having the Ethernet cable connected, the NIC would not show up at all, as in it wouldn’t be visible on the PCI bus. This is because of very aggressive power saving. The problem with this power saving tactic is that as far as I know, PCI wasn’t really designed with hot plug capability in mind, and powering down a chip to the level where it’s not visible on the PCI bus anymore, is more or less equivalent to PCI Hot Plug.

Early server solved this issue by having a special chip on the motherboard the handle the PCI Hot Plug events. Later on this was more or less standardized by using ACPI to handle this for laptops and possibly some desktop computers. And indeed the HP Mini needs ACPI PCI Hot Plug support to allow the Yukon 2 chip to be detected on the PCI bus after it’s been booted.

Somehow Ubuntu does not “detect” ACPI PCI Hot Plug is required and does not load the appropriate module. Luckily this is easily fixed by adding “acpiphp” to “/etc/modules”, and presto the Yukon 2 works as expected even if no Ethernet cable was attached during boot.