Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
9.2.8 Relationship to Backlight Control Methods
The Brightness Control Levels (_BCL) method – described in section 0 – can be used to indicate
user-selectable display brightness levels. The information provided by this method indicates the
available display brightness settings, the recommended default brightness settings for AC and DC
operation, and the absolute maximum and minimum brightness settings. These values indirectly
influence the operation of the OSPM’s ALS policy.
Display brightness adjustments produced by ALS policy are relative to the current user backlight
setting, and the resulting absolute value must be mapped (rounded) to one of the levels specified in
_BCL. This introduces the requirement for fine-grain display brightness control in order to achieve a
responsive ALS system – which typically materializes as a need for additional entries in the _BCL
list in order to provide reasonable resolution to the OS (e.g. 3-10% granularity). Note that user
brightness controls (e.g. hotkeys) are not required to make use of all levels specified in _BCL.
9.3 Battery Device
A battery device is required to either have an ACPI Smart Battery Table or a Control Method Battery
interface. In the case of an ACPI Smart Battery Table, the Definition Block needs to include a Bus/
Device Package for the SMBus host controller. This will install an OS specific driver for the SMBus,
which in turn will locate the Smart Battery System Manager or Smart Battery Selector and Smart
Battery Charger SMBus devices.
The Control Method Battery interface is defined in Section 10.2, “Control Method Batteries.”
9.4 Control Method Lid Device
Platforms containing lids convey lid status (open / closed) to OSPM using a Control Method Lid
Device.
To implement a control method lid device, AML code should issue a Notify(lid_device,
0x80) for the device whenever the lid status has changed. The _LID control method for the lid
device must be implemented to report the current state of the lid as either opened or closed.
The lid device can support _PRW and _PSW methods to select the wake functions for the lid when
the lid transitions from closed to opened.
The Plug and Play ID of an ACPI control method lid device is PNP0C0D.
Table 9-256 Control Method Lid Device
Object
_LID
Description
Returns the current status of the lid.
9.4.1 _LID
Evaluates to the current status of the lid.
Arguments:
None
506 April, 2015 Version 6.0