Set up device tree for PCI bus

[Hommel, Thomas (GE Indust, GE Fanuc)]

Hi all,
I'm wondering how to set up a proper device tree for a PCI bus. The bus
has a tree-like structure with several bridges and can be extended
dynamically (by adding PMC/XMC modules).

The structure looks like this:

                           ----------------------
                           |      MPC8641       |
                           |                    |
                           |     BDF 0:0:0      |
                           ----------------------
                                      |
                                      |Bus #1
                                      |PCIe 8x
                                      |
                -----------------------------------------------
                | PCIe switch         |                       |
                |               -------------                 |
                |               | BDF 1:0:0 |                 |   
                |               -------------                 |
                |                     |Bus #2                 |
                |       -----------------------------         |
                |       |             |             |         |
                |  -----------  ------------   -----------    |
                |  |BDF 2:1:0|  |BDF 2:2:0 |   |BDF 2:3:0|    |
                |  -----------  ------------   -----------    |
                |       |Bus #3       |Bus #5       |Bus #6   |
                |       |PCIe 4x      |PCIe 2x      |PCIe 2x  |
                -----------------------------------------------
                        |             |             |
                   -----------  ------------   -----------    
                   |Bridge   |  |Expansion |   |SATA     |    
                   |BDF 3:0:0|  |Slot      |   |BDF 6:0:0|    
                   -----------  ------------   -----------    
                        |
                        |Bus #4
                        |PCI-X
             ----------------------
             |                    |
        ------------         ------------ 
        |VME Bridge|         |PMC Slot  |     
        |BDF 4:e:0 |         |BDF 4:c:0 |     
        ------------         ------------     

A problem is that the modules in the Expansion/PMC slot can contain more
bridges and therefore the bus numbering isn't fixed. For example, if the
PMC adds one more bus, #5 becomes #6 and #6 becomes #7.
Can I assign fixed resources for all the bridge parts of the system?

Thanks
Thomas