Advanced Configuration and Power Interface Specification

Device Configuration
Note: The OS only runs _REG methods that appear in the same scope as operation region declarations
that use the operation region type that has just been made available. For example, _REG in the
EC device would not be run when the PCI bus driver is loaded since the operation regions
declared under EC do not use any of the operation region types made available by the PCI driver
(namely, config space, I/O, and memory).
6.5.5 _BBN (Base Bus Number)
For multi-root PCI platforms, the _BBN object evaluates to the PCI bus number that the BIOS
assigns. This is needed to access a PCI_Config operation region for the specific bus. The _BBN
object is located under a PCI host bridge and must be unique for every host bridge within a segment
since it is the PCI bus number.
Arguments:
None
Return Value:
An Integer that contains the PCI bus number. The lower 8 bits of _BBN returned integer is the PCI
Base Bus number. Other bits are reserved.
6.5.6 _SEG (Segment)
The optional _SEG object is located under a PCI host bridge and evaluates to an integer that
describes the PCI Segment Group (see PCI Firmware Specification v3.0). If _SEG does not exist,
OSPM assumes that all PCI bus segments are in PCI Segment Group 0.
Arguments:
None
Return Value:
PCI Segment Group is purely a software concept managed by system firmware and used by OSPM.
It is a logical collection of PCI buses (or bus segments). There is no tie to any physical entities. It is
a way to logically group the PCI bus segments and PCI Express Hierarchies. _SEG is a level higher
than _BBN.
PCI Segment Group supports more than 256 buses in a system by allowing the reuse of the PCI bus
numbers. Within each PCI Segment Group, the bus numbers for the PCI buses must be unique. PCI
buses in different PCI Segment Group are permitted to have the same bus number.
A PCI Segment Group contains one or more PCI host bridges.
The lower 16 bits of _SEG returned integer is the PCI Segment Group number. Other bits are
reserved.
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