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Protocols — PCI Bus Support
Version 1.10 12/01/02 12-3
A PCI Host Bridge and PCI Root Bridge are different than a PCI Segment. A PCI Segment is a
collection of up to 256 PCI busses that share the same PCI Configuration Space. Depending on
the chipset, a single EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL
may abstract a portion of a PCI
Segment, or an entire PCI Segment. A PCI Host Bridge may produce one or more PCI Root
Bridges. When a PCI Host Bridge produces multiple PCI Root Bridges, it is possible to have
more than one PCI Segment.
PCI Root Bridge I/O Protocol instances are either produced by the system firmware or by an EFI
driver. When a PCI Root Bridge I/O Protocol is produced, it is placed on a device handle along
with an EFI Device Path Protocol instance. Figure 12-2 shows a sample device handle for a PCI
Root Bridge Controller that includes an instance of the EFI_DEVICE_PATH_PROTOCOL
and the
EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL. Section 12.2 describes the PCI Root Bridge I/O
Protocol in detail, and Section 12.2.1 describes how to build device paths for PCI Root Bridges.
The EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL does not abstract access to the chipset-specific
registers that are used to manage a PCI Root Bridge. This functionality is hidden within the system
firmware or the EFI driver that produces the handles that represent the PCI Root Bridges.
OM13151
Device Handle
EFI_DEVICE_PATH_PROTOCOL
EFI_PCI_ROOT_BRIDGE_PROTOCOL
Figure 12-2. Device Handle for a PCI Root Bridge Controller