Now we tackle pci_add_new_bus and pci_scan_bridge.  The hotplug code
  currently uses this, but I'd like it to die off; pci_scan_bridge()
  should be used to scan behind bridges.  This may mean hotplug needs
  some changes to pci_scan_bridge - if so, we need to find out what
  changes are required and fix it.

  pci_alloc_child_bus() does what pci_add_new_bus() did, except it
  doesn't attach the new bus to the parents list of child buses.  The
  only way this bus can be reached from the parent bus is by scanning
  the parents devices list, and locating a device with a non-NULL
  subordinate bus.  The only code which should be doing this is the
  PCI code.

  Since the new bus will have an empty list head for bus->node, we can
  detect unattached buses prety easily.  (see pci-3.diff.)

  pci_scan_bridge() changes slightly - we use our new pci_scan_child_bus()
  function from pci-3.diff, which doesn't attach devices to the global
  tree.  This means callers of pci_scan_child_bus() and pci_scan_bridge()
  (ie, hotplug) will need to call pci_bus_add_devices().