Documentation/wmi/acpi-interface.rst - linux/kernel/git/gregkh/tty - Git at Google

 .. SPDX-License-Identifier: GPL-2.0-or-later

 ==================
 ACPI WMI interface
 ==================

 The ACPI WMI interface is a proprietary extension of the ACPI specification made
 by Microsoft to allow hardware vendors to embed WMI (Windows Management Instrumentation)
 objects inside their ACPI firmware. Typical functions implemented over ACPI WMI
 are hotkey events on modern notebooks and configuration of BIOS options.

 PNP0C14 ACPI device
 -------------------

 Discovery of WMI objects is handled by defining ACPI devices with a PNP ID
 of ``PNP0C14``. These devices will contain a set of ACPI buffers and methods
 used for mapping and execution of WMI methods and/or queries. If there exist
 multiple of such devices, then each device is required to have a
 unique ACPI UID.

 _WDG buffer
 -----------

 The ``_WDG`` buffer is used to discover WMI objects and is required to be
 static. Its internal structure consists of data blocks with a size of 20 bytes,
 containing the following data:

 ======= =============== =====================================================
 Offset  Size (in bytes) Content
 ======= =============== =====================================================
 0x00    16              128 bit Variant 2 object GUID.
 0x10    2               2 character method ID or single byte notification ID.
 0x12    1               Object instance count.
 0x13    1               Object flags.
 ======= =============== =====================================================

 The WMI object flags control whether the method or notification ID is used:

 - 0x1: Data block is expensive to collect.
 - 0x2: Data block contains WMI methods.
 - 0x4: Data block contains ASCIZ string.
 - 0x8: Data block describes a WMI event, use notification ID instead
   of method ID.

 Each WMI object GUID can appear multiple times inside a system.
 The method/notification ID is used to construct the ACPI method names used for
 interacting with the WMI object.

 WQxx ACPI methods
 -----------------

 If a data block does not contain WMI methods, then its content can be retrieved
 by this required ACPI method. The last two characters of the ACPI method name
 are the method ID of the data block to query. Their single parameter is an
 integer describing the instance which should be queried. This parameter can be
 omitted if the data block contains only a single instance.

 WSxx ACPI methods
 -----------------

 Similar to the ``WQxx`` ACPI methods, except that it is optional and takes an
 additional buffer as its second argument. The instance argument also cannot
 be omitted.

 WMxx ACPI methods
 -----------------

 Used for executing WMI methods associated with a data block. The last two
 characters of the ACPI method name are the method ID of the data block
 containing the WMI methods. Their first parameter is a integer describing the
 instance which methods should be executed. The second parameter is an integer
 describing the WMI method ID to execute, and the third parameter is a buffer
 containing the WMI method parameters. If the data block is marked as containing
 an ASCIZ string, then this buffer should contain an ASCIZ string. The ACPI
 method will return the result of the executed WMI method.

 WExx ACPI methods
 -----------------

 Used for optionally enabling/disabling WMI events, the last two characters of
 the ACPI method are the notification ID of the data block describing the WMI
 event as hexadecimal value. Their first parameter is an integer with a value
 of 0 if the WMI event should be disabled, other values will enable
 the WMI event.

 Those ACPI methods are always called even for WMI events not registered as
 being expensive to collect to match the behavior of the Windows driver.

 WCxx ACPI methods
 -----------------
 Similar to the ``WExx`` ACPI methods, except that instead of WMI events it controls
 data collection of data blocks registered as being expensive to collect. Thus the
 last two characters of the ACPI method name are the method ID of the data block
 to enable/disable.

 Those ACPI methods are also called before setting data blocks to match the
 behavior of the Windows driver.

 _WED ACPI method
 ----------------

 Used to retrieve additional WMI event data, its single parameter is a integer
 holding the notification ID of the event. This method should be evaluated every
 time an ACPI notification is received, since some ACPI implementations use a
 queue to store WMI event data items. This queue will overflow after a couple
 of WMI events are received without retrieving the associated WMI event data.

 Conversion rules for ACPI data types
 ------------------------------------

 Consumers of the ACPI-WMI interface use binary buffers to exchange data with the WMI driver core,
 with the internal structure of the buffer being only know to the consumers. The WMI driver core is
 thus responsible for converting the data inside the buffer into an appropriate ACPI data type for
 consumption by the ACPI firmware. Additionally, any data returned by the various ACPI methods needs
 to be converted back into a binary buffer.

 The layout of said buffers is defined by the MOF description of the WMI method or data block in
 question [1]_:

 =============== ======================================================================= =========
 Data Type       Layout                                                                  Alignment
 =============== ======================================================================= =========
 ``string``      Starts with an unsigned 16-bit little endian integer specifying         2 bytes
                 the length of the string data in bytes, followed by the string data
                 encoded as UTF-16LE with **optional** NULL termination and padding.
                 Keep in mind that some firmware implementations might depend on the
                 terminating NULL character to be present. Also the padding should
                 always be performed with NULL characters.
 ``boolean``     Single byte where 0 means ``false`` and nonzero means ``true``.         1 byte
 ``sint8``       Signed 8-bit integer.                                                   1 byte
 ``uint8``       Unsigned 8-bit integer.                                                 1 byte
 ``sint16``      Signed 16-bit little endian integer.                                    2 bytes
 ``uint16``      Unsigned 16-bit little endian integer.                                  2 bytes
 ``sint32``      Signed 32-bit little endian integer.                                    4 bytes
 ``uint32``      Unsigned 32-bit little endian integer.                                  4 bytes
 ``sint64``      Signed 64-bit little endian integer.                                    8 bytes
 ``uint64``      Unsigned 64-bit little endian integer.                                  8 bytes
 ``datetime``    A fixed-length 25-character UTF-16LE string with the format             2 bytes
                 *yyyymmddhhmmss.mmmmmmsutc* where *yyyy* is the 4-digit year, *mm* is
                 the 2-digit month, *dd* is the 2-digit day, *hh* is the 2-digit hour
                 based on a 24-hour clock, *mm* is the 2-digit minute, *ss* is the
                 2-digit second, *mmmmmm* is the 6-digit microsecond, *s* is a plus or
                 minus character depending on whether *utc* is a positive or negative
                 offset from UTC (or a colon if the date is an interval). Unpopulated
                 fields should be filled with asterisks.
 =============== ======================================================================= =========

 Arrays should be aligned based on the alignment of their base type, while objects should be
 aligned based on the largest alignment of an element inside them.

 All buffers returned by the WMI driver core are 8-byte aligned. When converting ACPI data types
 into such buffers the following conversion rules apply:

 =============== ============================================================
 ACPI Data Type  Converted into
 =============== ============================================================
 Buffer          Copied as-is.
 Integer         Converted into a ``uint32``.
 String          Converted into a ``string`` with a terminating NULL character
                 to match the behavior the of the Windows driver.
 Package         Each element inside the package is converted with alignment
                 of the resulting data types being respected. Nested packages
                 are not allowed.
 =============== ============================================================

 The Windows driver does attempt to handle nested packages, but this results in internal data
 structures (``_ACPI_METHOD_ARGUMENT_V1``) erroneously being copied into the resulting buffer.
 ACPI firmware implementations should thus not return nested packages from ACPI methods
 associated with the ACPI-WMI interface.

 References
 ==========

 .. [1] https://learn.microsoft.com/en-us/windows-hardware/drivers/kernel/driver-defined-wmi-data-items
	.. SPDX-License-Identifier: GPL-2.0-or-later

	==================
	ACPI WMI interface
	==================

	The ACPI WMI interface is a proprietary extension of the ACPI specification made
	by Microsoft to allow hardware vendors to embed WMI (Windows Management Instrumentation)
	objects inside their ACPI firmware. Typical functions implemented over ACPI WMI
	are hotkey events on modern notebooks and configuration of BIOS options.

	PNP0C14 ACPI device
	-------------------

	Discovery of WMI objects is handled by defining ACPI devices with a PNP ID
	of ``PNP0C14``. These devices will contain a set of ACPI buffers and methods
	used for mapping and execution of WMI methods and/or queries. If there exist
	multiple of such devices, then each device is required to have a
	unique ACPI UID.

	_WDG buffer
	-----------

	The ``_WDG`` buffer is used to discover WMI objects and is required to be
	static. Its internal structure consists of data blocks with a size of 20 bytes,
	containing the following data:

	======= =============== =====================================================
	Offset Size (in bytes) Content
	======= =============== =====================================================
	0x00 16 128 bit Variant 2 object GUID.
	0x10 2 2 character method ID or single byte notification ID.
	0x12 1 Object instance count.
	0x13 1 Object flags.
	======= =============== =====================================================

	The WMI object flags control whether the method or notification ID is used:

	- 0x1: Data block is expensive to collect.
	- 0x2: Data block contains WMI methods.
	- 0x4: Data block contains ASCIZ string.
	- 0x8: Data block describes a WMI event, use notification ID instead
	of method ID.

	Each WMI object GUID can appear multiple times inside a system.
	The method/notification ID is used to construct the ACPI method names used for
	interacting with the WMI object.

	WQxx ACPI methods
	-----------------

	If a data block does not contain WMI methods, then its content can be retrieved
	by this required ACPI method. The last two characters of the ACPI method name
	are the method ID of the data block to query. Their single parameter is an
	integer describing the instance which should be queried. This parameter can be
	omitted if the data block contains only a single instance.

	WSxx ACPI methods
	-----------------

	Similar to the ``WQxx`` ACPI methods, except that it is optional and takes an
	additional buffer as its second argument. The instance argument also cannot
	be omitted.

	WMxx ACPI methods
	-----------------

	Used for executing WMI methods associated with a data block. The last two
	characters of the ACPI method name are the method ID of the data block
	containing the WMI methods. Their first parameter is a integer describing the
	instance which methods should be executed. The second parameter is an integer
	describing the WMI method ID to execute, and the third parameter is a buffer
	containing the WMI method parameters. If the data block is marked as containing
	an ASCIZ string, then this buffer should contain an ASCIZ string. The ACPI
	method will return the result of the executed WMI method.

	WExx ACPI methods
	-----------------

	Used for optionally enabling/disabling WMI events, the last two characters of
	the ACPI method are the notification ID of the data block describing the WMI
	event as hexadecimal value. Their first parameter is an integer with a value
	of 0 if the WMI event should be disabled, other values will enable
	the WMI event.

	Those ACPI methods are always called even for WMI events not registered as
	being expensive to collect to match the behavior of the Windows driver.

	WCxx ACPI methods
	-----------------
	Similar to the ``WExx`` ACPI methods, except that instead of WMI events it controls
	data collection of data blocks registered as being expensive to collect. Thus the
	last two characters of the ACPI method name are the method ID of the data block
	to enable/disable.

	Those ACPI methods are also called before setting data blocks to match the
	behavior of the Windows driver.

	_WED ACPI method
	----------------

	Used to retrieve additional WMI event data, its single parameter is a integer
	holding the notification ID of the event. This method should be evaluated every
	time an ACPI notification is received, since some ACPI implementations use a
	queue to store WMI event data items. This queue will overflow after a couple
	of WMI events are received without retrieving the associated WMI event data.

	Conversion rules for ACPI data types
	------------------------------------

	Consumers of the ACPI-WMI interface use binary buffers to exchange data with the WMI driver core,
	with the internal structure of the buffer being only know to the consumers. The WMI driver core is
	thus responsible for converting the data inside the buffer into an appropriate ACPI data type for
	consumption by the ACPI firmware. Additionally, any data returned by the various ACPI methods needs
	to be converted back into a binary buffer.

	The layout of said buffers is defined by the MOF description of the WMI method or data block in
	question [1]_:

	=============== ======================================================================= =========
	Data Type Layout Alignment
	=============== ======================================================================= =========
	``string`` Starts with an unsigned 16-bit little endian integer specifying 2 bytes
	the length of the string data in bytes, followed by the string data
	encoded as UTF-16LE with optional NULL termination and padding.
	Keep in mind that some firmware implementations might depend on the
	terminating NULL character to be present. Also the padding should
	always be performed with NULL characters.
	``boolean`` Single byte where 0 means ``false`` and nonzero means ``true``. 1 byte
	``sint8`` Signed 8-bit integer. 1 byte
	``uint8`` Unsigned 8-bit integer. 1 byte
	``sint16`` Signed 16-bit little endian integer. 2 bytes
	``uint16`` Unsigned 16-bit little endian integer. 2 bytes
	``sint32`` Signed 32-bit little endian integer. 4 bytes
	``uint32`` Unsigned 32-bit little endian integer. 4 bytes
	``sint64`` Signed 64-bit little endian integer. 8 bytes
	``uint64`` Unsigned 64-bit little endian integer. 8 bytes
	``datetime`` A fixed-length 25-character UTF-16LE string with the format 2 bytes
	yyyymmddhhmmss.mmmmmmsutc where yyyy is the 4-digit year, mm is
	the 2-digit month, dd is the 2-digit day, hh is the 2-digit hour
	based on a 24-hour clock, mm is the 2-digit minute, ss is the
	2-digit second, mmmmmm is the 6-digit microsecond, s is a plus or
	minus character depending on whether utc is a positive or negative
	offset from UTC (or a colon if the date is an interval). Unpopulated
	fields should be filled with asterisks.
	=============== ======================================================================= =========

	Arrays should be aligned based on the alignment of their base type, while objects should be
	aligned based on the largest alignment of an element inside them.

	All buffers returned by the WMI driver core are 8-byte aligned. When converting ACPI data types
	into such buffers the following conversion rules apply:

	=============== ============================================================
	ACPI Data Type Converted into
	=============== ============================================================
	Buffer Copied as-is.
	Integer Converted into a ``uint32``.
	String Converted into a ``string`` with a terminating NULL character
	to match the behavior the of the Windows driver.
	Package Each element inside the package is converted with alignment
	of the resulting data types being respected. Nested packages
	are not allowed.
	=============== ============================================================

	The Windows driver does attempt to handle nested packages, but this results in internal data
	structures (``_ACPI_METHOD_ARGUMENT_V1``) erroneously being copied into the resulting buffer.
	ACPI firmware implementations should thus not return nested packages from ACPI methods
	associated with the ACPI-WMI interface.

	References
	==========

	.. [1] https://learn.microsoft.com/en-us/windows-hardware/drivers/kernel/driver-defined-wmi-data-items