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diff --git a/Documentation/wmi/acpi-interface.rst b/Documentation/wmi/acpi-interface.rst index 1ef003b033bf..4657101c528a 100644 --- a/Documentation/wmi/acpi-interface.rst +++ b/Documentation/wmi/acpi-interface.rst @@ -104,3 +104,71 @@ 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 |