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+PCI bus bridges have standardized Device Tree bindings:
+
+PCI Bus Binding to: IEEE Std 1275-1994
+http://www.devicetree.org/open-firmware/bindings/pci/pci2_1.pdf
+
+And for the interrupt mapping part:
+
+Open Firmware Recommended Practice: Interrupt Mapping
+http://www.devicetree.org/open-firmware/practice/imap/imap0_9d.pdf
+
+Additionally to the properties specified in the above standards a host bridge
+driver implementation may support the following properties:
+
+- linux,pci-domain:
+ If present this property assigns a fixed PCI domain number to a host bridge,
+ otherwise an unstable (across boots) unique number will be assigned.
+ It is required to either not set this property at all or set it for all
+ host bridges in the system, otherwise potentially conflicting domain numbers
+ may be assigned to root buses behind different host bridges. The domain
+ number for each host bridge in the system must be unique.
+- max-link-speed:
+ If present this property specifies PCI gen for link capability. Host
+ drivers could add this as a strategy to avoid unnecessary operation for
+ unsupported link speed, for instance, trying to do training for
+ unsupported link speed, etc. Must be '4' for gen4, '3' for gen3, '2'
+ for gen2, and '1' for gen1. Any other values are invalid.