+In this example, the root PCI bus node is the "/pci" which matches "pci-x86"
+driver. It has a subnode "pcie@17,0" with driver "pci-bridge". "pcie@17,0"
+also has subnode "topcliff@0,0" which is a "pci-bridge" too. Under that bridge,
+a PCI UART device "uart@a,1" is described. This exactly reflects the hardware
+bus hierarchy: on the root PCI bus, there is a PCIe root port which connects
+to a downstream device Topcliff chipset. Inside Topcliff chipset, it has a
+PCIe-to-PCI bridge and all the chipset integrated devices like the PCI UART
+device are on the PCI bus. Like other devices in the device tree, if we want
+to bind PCI devices before relocation, "u-boot,dm-pre-reloc" must be declared
+in each of these nodes.
+
+If PCI devices are not listed in the device tree, U_BOOT_PCI_DEVICE can be used
+to specify the driver to use for the device. The device tree takes precedence
+over U_BOOT_PCI_DEVICE. Plese note with U_BOOT_PCI_DEVICE, only drivers with
+DM_FLAG_PRE_RELOC will be bound before relocation. If neither device tree nor
+U_BOOT_PCI_DEVICE is provided, the built-in driver (either pci_bridge_drv or
+pci_generic_drv) will be used.