4. Boot Arguments to Control PCI Bus Behaviour (`pci=')

The `pci=' argument (not avail. in v2.0 kernels) can be used to change the behaviour of PCI bus device probing and device behaviour. Firstly the file linux/drivers/pci/pci.c checks for architecture independent pci= options. The remaining allowed arguments are handled in linux/arch/???/kernel/bios32.c and are listed below for ???=i386.

4.1 The `pci=bios' and `pci=nobios' Arguments

These are used to set/clear the flag indicating that the PCI probing is to take place via the PCI BIOS. The default is to use the BIOS.

4.2 The `pci=conf1' and `pci=conf2' Arguments

If PCI direct mode is enabled, the use of these enables either configuration Type 1 or Type 2. These implicitly clear the PCI BIOS probe flag (i.e. `pci=nobios') too.

4.3 The `pci=io=' Argument

If you get a message like PCI: Unassigned IO space for.../ then you may need to supply an I/O value with this option. From the source:

``Several BIOS'es forget to assign addresses to I/O ranges. We try to fix it here, expecting there are free addresses starting with 0x5800. Ugly, but until we come with better resource management, it's the only simple solution.''

4.4 The `pci=nopeer' Argument

This disables the default peer bridge fixup, which according to the source does the following:

``In case there are peer host bridges, scan bus behind each of them. Although several sources claim that the host bridges should have header type 1 and be assigned a bus number as for PCI2PCI bridges, the reality doesn't pass this test and the bus number is usually set by BIOS to the first free value.''

4.5 The `pci=nosort' Argument

Using this argument instructs the kernel to not sort the PCI devices during the probing phase.

4.6 The `pci=off' Argument

Using this option disables all PCI bus probing. Any device drivers that make use of PCI functions to find and initialize hardware will most likely fail to work.

4.7 The `pci=reverse' Argument

This option will reverse the ordering of the PCI devices on that PCI bus.