PCI Probing

Of the six PCI buses on the Ultra 450 system , bus 0 (/pci@1f,4000 in the device tree) is unique in that it is the only PCI bus that contains motherboard (non plug-in) devices such as standard Ethernet and SCSI controllers. By definition, these devices cannot be unplugged and swapped to change the order in which they are probed. To control the probing order of these devices, the system provides the NVRAM variable pci0-probe-list. This variable controls both the probing order and exclusion of devices on PCI bus 0. The values in the pci0-probe-list are defined in the following table.

The values in this list are based on the PCI device number and do not refer to the back panel slot numbering scheme of 1-10.

In the following example, the pci0-probe-list variable is used to define a probing order of 3-4, while excluding from the probe list the on-board SCSI controller for removable media devices and the external SCSI port.

ok setenv pci0-probe-list 3,4

The probing order of the other five PCI buses (PCI slots 1 through 9) is not subject to user control. These slots are always probed in the following order: 5-3-2-1-4-9-8-7-6. However, a list of PCI slots can be excluded from probing via the NVRAM variable pci-slot-skip-list. In the following example, the pci-slot-skip-list variable is used to exclude back panel slots 3 and 8 from the PCI probe list.

ok setenv pci-slot-skip-list 3,8

The values in the pci-slot-skip-list correspond to the back panel numbering scheme of 1-10. If slot 10 is in this list, then it will be excluded from probing even if pci0-probe-list includes device number 4 (back panel slot 10).