how hotplug devices onto pcie-to-pci-bridge

[longguang.yue]

Hi, all
  I have add two pcie-to-pci-bridge controllers, how hotplug devices onto this 
two controllers?  and libvirt knows to plug onto pci-bridge when there are no 
pcie-ports.
defaultly libvirt plugs devices onto pcie-port. 


thanks