Systems based on the Intel 450NX chipset may experience issues where devices aren't recognised that lead to drivers failing, unhandled IRQs, and other serious boot failures. The issue is caused because this chipset has 3 PCI root buses. When it was first released some operating systems (read: Windows NT) didn't always correctly discover the 2nd and 3rd PCI buses. As a result the PCI BIOS tables were 'hacked' to have a fake bridge device on PCI bus 0 that points to the same bus number as the 1st bus so they would be scanned correctly by the OS.
As a result, in a well-behaved OS the 2nd and 3rd PCI buses would be scanned twice. Once as secondaries of the 1st bus, and then as root buses in their own right. This caused problems with devices being discovered twice.
Unfortunately, the user's kernel-log report is misleading since the bus has already been found to be registered and therefore ignored. The situation can be worked around by booting with "pci=noacpi".
A fix-up for all i450N chipsets was introduced in arch/i386/pci/fixups.c::pci_fixup_i450nx(). Note: arch/i386 was refactored to arch/x86/ subsequently. The fix-up checks the PCI config for the subsidiary buses and if it finds them scans them. This adds them to the root_pci_bus list. Later in the boot process the ACPI/PCI code reads the ACPI DSDT table, finds the PCI bus entries (PNP0A03) and tries to scan them again, leading to the kernel BUG.
This patch ensures that buses already scanned are recognised rather than ignored.
TJ.
Ubuntu Kernel ACPI Team.
SRU Justification:
Impact: Some machines will not boot with ACPI enabled
Patch Description: Check that the root PCI bus has already been scanned.
Patch: http://
Test Case: see bug desciption