acpi=off otherwise machine doesnt boot

[Maaz]

Thanks Dear Mike Stroyan .
whats this kernel parameter does pci=nommconf... ? what is it for ?

[Mike Stroyan · Accepted solution]

The pci=nommconf boot option disables one specific feature that is among the many that are disabled by the acpi=off option.
The MMCONFIG feature uses a recently added ACPI MCFG table that provides another way to describe PCI devices' configuration to the OS. MMCONFIG changes from IO mapping PCI devices to memory mapping PCI devices.
There are other older ways to identify and access PCI devices. It seems that some systems and BIOS revisions have trouble with linux trying to use MMCONFIG, while others have trouble with trying to use the "bios" or "conf1" or "conf2" methods. The MMCONFIG mechanism is still fairly new in linux. And the ACPI MCFG feature itself is new. Because ACPI MCFG is ignored by windows releases prior to vista it may not have had much testing. So trouble with MMCONFIG may be due to problems in the kernel or problems in the BIOS, or disagreement in interpreting specifications.
Forcing pci=nommconf means that the PCI devices are iomapped in the old way instead of memory mapped in the new way.