
- every pci device which implements _PRT acpi method is considered to be a pci-to-pci bridge - acpi driver constructs a hierarchy of pci-to-pci bridges - when pci driver identifies a pci-to-pci bridge it tells acpi driver what is the primary and the secondary bus for this device - when pci requests IRQ routing information from acpi, it passes the bus number too to be able to identify the device accurately