Advanced Configuration and Power Interface Specification

Device Configuration
other governing specifications describe superseding device specific _OSC capabilities and / or
preclusions.
_OSC enables the platform to configure its ACPI namespace representation and object evaluations
to match the capabilities of OSPM. This enables legacy operating system support for platforms with
new features that make use of new namespace objects that if exposed would not be evaluated when
running a legacy OS. _OSC provides the capability to transition the platform to native operating
system support of new features and capabilities when available through dynamic namespace
reconfiguration. _OSC also allows devices with Compatible IDs to provide superset functionality
when controlled by their native (For example, _HID matched) driver as appropriate objects can be
exposed accordingly as a result of OSPM’s evaluation of _OSC.
Arguments: (4)
Arg0 – A Buffer containing a UUID
Arg1 – An Integer containing a Revision ID of the buffer format
Arg2 – An Integer containing a count of entries in Arg3
Arg3 – A Buffer containing a list of DWORD capabilities
Return Value:
A Buffer containing a list of capabilities
Argument Information
Arg0: UUID – Universal Unique Identifier (16 Byte Buffer) used by the platform in conjunction
with Revision ID to ascertain the format of the Capabilities buffer.
Arg1: Revision ID – The revision of the Capabilities Buffer format. The revision level is specific to
the UUID.
Arg2: Count – Number of DWORDs in the Capabilities Buffer in Arg3
Arg3: Capabilities Buffer – Buffer containing the number of DWORDs indicated by Count. The first
DWORD of this buffer contains standard bit definitions as described below. Subsequent DWORDs
contain UUID-specific bits that convey to the platform the capabilities and features supported by
OSPM. Successive revisions of the Capabilities Buffer must be backwards compatible with earlier
revisions. Bit ordering cannot be changed.
Capabilities Buffers are device-specific and as such are described under specific device definitions.
See Section 9, “ACPI Devices and Device Specific Objects” for any _OSC definitions for ACPI
devices. The format of the Capabilities Buffer and behavior rules may also be specified by OEMs
and IHVs for custom devices and other interface or device governing bodies for example, the PCI
SIG.
The first DWORD in the capabilities buffer is used to return errors defined by _OSC. This DWORD
must always be present and may not be redefined/reused by unique interfaces utilizing _OSC.
• Bit [0]- Query Support Flag. If set, the _OSC invocation is a query by OSPM to determine or
negotiate with the platform the combination of capabilities for which OSPM may take control.
In this case, OSPM sets bits in the subsequent DWORDs to specify the capabilities for which
OSPM intends to take control. If clear, OSPM is attempting to take control of the capabilities
corresponding to the bits set in subsequent DWORDs. OSPM may only take control of
capabilities as indicated by the platform by the result of the query.
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