Intel Extensible Firmware Interface - Manual (Page 454)

Extensible Firmware Interface Specification
12-36 12/01/02 Version 1.10
Status Codes Returned
EFI_SUCCESS If Supports is not NULL , then the attributes that the PCI root
bridge supports is returned in Supports . If Attributes is
not NULL , then the attributes that the PCI root bridge is currently
using is returned in Attributes .
EFI_INVALID_PARAMETER Both Supports and Attributes are NULL .