Intel Extensible Firmware Interface - Manual (Page 241)

Protocols — Device Path Protocol
Version 1.10 12/01/02 8-21
Support of root PCI bridges requires special rules in the EFI Device Path. A root PCI bridge is a
PCI device usually contained in a chipset that consumes a proprietary bus and produces a PCI bus.
In typical desktop and mobile systems there is only one root PCI bridge. On larger server systems
there are typically multiple root PCI bridges. The operation of root PCI bridges is not defined in
any current PCI specification. A root PCI bridge should not be confused with a PCI to PCI bridge
that both consumes and produces a PCI bus. The operation and configuration of PCI to PCI bridges
is fully specified in current PCI specifications.
Root PCI bridges will use the plug and play ID of PNP0A03, This will be stored in the ACPI
Device Path _HID field, or in the Expanded ACPI Device Path _CID field to match the ACPI name
space. The _UID in the ACPI Device Path structure must match the _UID in the ACPI name space.
8.4.3 Rules with ACPI _ADR
If a device in the ACPI name space can be completely described by a _ADR object then it will map
to an EFI ACPI, Hardware, or Message Device Path structure. A _ADR method implies a bus with
a standard enumeration algorithm. If the ACPI device has a _ADR and a _CRS method, then it
should also have a _HID method and follow the rules for using _HID.
Table 8-31 relates the ACPI_ADR bus definition to the EFI Device Path:
Table 8-31. ACPI _ADR to EFI Device Path Mapping
ACPI _ADR Bus EFI Device Path
EISA Not supported
Floppy Bus ACPI Device Path: _HID PNP0604, _UID drive select encoding 0-3
IDE Controller ATAPI Message Device Path: Maser/Slave : LUN
IDE Channel ATAPI Message Device Path: Maser/Slave : LUN
PCI PCI Hardware Device Path
PCMCIA Not Supported
PC CARD PC CARD Hardware Device Path
SMBus Not Supported