Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
• Bit [1] – Always clear (0).
• Bit [2] – Always clear (0).
• Bit [3] – Always clear (0).
• All others – reserved.
Return Value Information
Capabilities Buffer (Buffer) – The platform acknowledges the Capabilities Buffer by returning a
buffer of DWORDs of the same length. Set bits indicate acknowledgement that OSPM may take
control of the capability and cleared bits indicate that the platform either does not support the
capability or that OSPM may not assume control.
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] – Reserved (not used)
• Bit [1] – _OSC failure. Platform Firmware was unable to process the request or query.
Capabilities bits may have been masked.
• Bit [2] – Unrecognized UUID. This bit is set to indicate that the platform firmware does not
recognize the UUID passed in via Arg0. Capabilities bits are preserved.
• Bit [3] – Unrecognized Revision. This bit is set to indicate that the platform firmware does not
recognize the Revision ID passed in via Arg1. Capabilities bits beyond those comprehended by
the firmware will be masked.
• Bit [4] – Capabilities Masked. This bit is set to indicate that capabilities bits set by driver
software have been cleared by platform firmware.
• All others – reserved.
Note: OSPM must not use the results of _OSC evaluation to choose a compatible device driver. OSPM
must use _HID, _CID, or native enumerable bus device identification mechanisms to select an
appropriate driver for a device.
The platform may issue a Notify(device, 0x08) to inform OSPM to re-evaluate _OSC when the
availability of feature control changes. Platforms must not rely, however, on OSPM to evaluate
_OSC after issuing a Notify for proper operation as OSPM cannot guarantee the presence of a target
entity to receive and process the Notify for the device. For example, a device driver for the device
may not be loaded at the time the Notify is signaled. Further, the issuance and processing rules for
notification of changes in the Capabilities Buffer is device specific. As such, the allowable behavior
is governed by device specifications either in Section 9, “ ACPI-Specific Device Objects”, for
ACPI-define devices, or other OEM, IHV, or device governing body’s’ device specifications.
It is permitted for _OSC to return all bits in the Capabilities Buffer cleared. An example of this is
when significant time is required to disable platform-based feature support. The platform may then
later issue a Notify to tell OSPM to re-evaluate _OSC to take over native control. This behavior is
also device specific but may also rely on specific OS capability.
In general, platforms should support both OSPM taking and relinquishing control of specific feature
support via multiple invocations of _OSC but the required behavior may vary on a per device basis.
314 April, 2015 Version 6.0