ACPI Debugging Guide in the Developer's Handbook. This is a good place to start if you are having problems with identifying hardware. (For instance, for many irq routing, hanging, device not accessible, panics, etc., you might want to see if disabling acpi fixes the problem in question. There are a large number of bad BIOS implementations out there; we put in hacks to work around as many as we can, but more are always needed.)