Advanced Configuration and Power Interface Specification

Processor Configuration and Control
8.4 Declaring Processors
Each processor in the system must be declared in the ACPI namespace in the \_SB scope.
Declaration of processors in the \_PR scope was only required for platforms desiring compatibility
with ACPI 1.0-based OSPM implementations. It is deprecated for all other uses. Processors are
declared via the ASL Device statement. Declarations via the ASL Processor statement are
deprecated. A Device definition for a processor is declared using the ACPI0007 hardware identifier
(HID). Processor configuration information is provided exclusively by objects in the processor
device's object list.
When the platform uses the APIC interrupt model, UID object values under a processor device are
used to associate processor devices with entries in the MADT.
Processor-specific objects may be declared within the processor device's scope. These objects serve
multiple purposes including processor performance state control. Other ACPI-defined device-related
objects are also allowed under the processor device's scope (for example, the unique identifier object
_UID mentioned above).
With device-like characteristics attributed to processors, it is implied that a processor device driver
will be loaded by OSPM to, at a minimum, process device notifications. OSPM will enumerate
processors in the system using the ACPI Namespace, processor-specific native identification
instructions, and the _HID method.
For more information on the declaration of the processor device object, see Section 19.6.30, "Device
(Declare Device Package)." Processor-specific child objects are described in the following sections.
ACPI 6.0 introduces the notion of processor containers. Processor containers are declared using the
Processor Container Device. A processor container can be used to describe a collection of
associated processors that share common resources, such as shared caches, and which have power
states that affect the processors in the collection. For more information see Section 8.4.3.1
"Processor Container Device”.
8.4.1 _PDC (Processor Driver Capabilities)
This optional object is a method that is used by OSPM to communicate to the platform the level of
processor power management support provided by OSPM. This object is a child object of the
processor. OSPM evaluates _PDC prior to evaluating any other processor power management
objects returning configuration information.
The _PDC object provides OSPM a mechanism to convey to the platform the capabilities supported
by OSPM for processor power management. This allows the platform to modify the ACPI
namespace objects returning configuration information for processor power management based on
the level of support provided by OSPM. Using this method provides a mechanism for OEMs to
provide support for new technologies on legacy OSes, while also allowing OSPM to leverage new
technologies on platforms capable of supporting them. This method is evaluated once during
processor device initialization, and will not be re-evaluated during resume from a sleep state
transition. The platform must preserve state information across S1-S3 sleep state transitions.
Arguments: (1)
Arg0 – A variable-length Buffer containing a list of capabilities as described below
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