Some bus drivers are required to produce the Bus Specific Driver Override Protocol. The driver model for a specific bus type must declare if this protocol is required or not. In general, this protocol applies only to bus types that provide containers for UEFI Drivers on their child devices.
At this time, the only bus type that is required to produce this protocol is PCI, and the container for drivers is the PCI option ROM. The PCI bus driver is required to produce the Bus Specific Driver Override Protocol for PCI devices that have an attached PCI option ROM if the PCI option ROM contains one or more loadable UEFI drivers. If a PCI option ROM is not present, or the PCI option ROM does not contain any loadable UEFI drivers, a Bus Specific Driver Override Protocol is not produced for that PCI device.