Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
hierarchy is herein referred to as a node. The processor container device is declared using the
hardware identifier (_HID) ACPI0010.
To aid support of operating systems which do not parse processor containers, a container can carry a
Compatible ID (_CID) of PNP0A05, which represents a generic container device (see Section 5.6.7)
A processor container declaration must supply a _UID method returning an ID that is unique in the
processor container hierarchy. A processor container must contain either other processor containers
or other processor devices declared within its scope. In addition, a processor container may also
contain the following methods in its scope:
Table 8-238 Processor Container Device Objects
Object Description
_LPI Declares local power states for the hierarchy node represented by the processor container
_RDI Declares power resource dependencies that affect system level power states
_STA Determines the status of a processor container. See Section 5.6.7,
_LPI may be present under a processor device, and is described in Section 8.4.4.3 _RDI can only be
present under a singular top level processor container object, and is described below.
ACPI allows the definition of more than one root level processor container. In other words, it is
possible to define multiple top level containers. For example, in a NUMA system if there are no idle
states or other objects that need to be encapsulated at the system level, multiple NUMA-node level
processor containers may be defined at the top level of the hierarchy.
Processor Container Device objects are only valid for implementations conforming to ACPI 6.0 or
higher. A platform can ascertain whether an operating system supports parsing of processor
container objects via the _OSC method (see Section 6.2.11.2).
8.4.4 Lower Power Idle States
ACPI 6.0 introduces Lower Power Idle states (LPI). This extends the specification to allow
expression of idle states that, like C-states, are selected by the OSPM when a processor goes idle, but
which may affect more than one processor, and may affect other system components. LPI extensions
in the specification leverage the processor container device, and in this way can express which parts
of the system are affected by a given LPI state.
LPI states are defined via the following objects:
• _LPI objects define the states themselves, and may be declared inside a processor or a processor
container device
• _RDI allows expressing constraints on LPI usage borne out of device usage
8.4.4.1 Hierarchical Idle States
Processor containers (Section 8.4.3.1) can be used in conjunction with _LPI (Section 8.4.4.3) to
describe idle states in a hierarchical manner. Within the processor hierarchy, each node has low
power states that are specific to that node. ACPI refers to states that are specific to a node in the
hierarchy as Local Power States. For example in the system depicted in Figure 8-46, the local power
states of CPU0 are clock gate, retention and power down.
436 April, 2015 Version 6.0