2024-04-21 12:11:45 -07:00
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.. SPDX-License-Identifier: GPL-2.0-or-later
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===================================================
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MSI WMI Platform Features driver (msi-wmi-platform)
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===================================================
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Introduction
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============
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Many MSI notebooks support various features like reading fan sensors. This features are controlled
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by the embedded controller, with the ACPI firmware exposing a standard ACPI WMI interface on top
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of the embedded controller interface.
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WMI interface description
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=========================
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The WMI interface description can be decoded from the embedded binary MOF (bmof)
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data using the `bmfdec <https://github.com/pali/bmfdec>`_ utility:
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::
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[WMI, Locale("MS\0x409"),
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Description("This class contains the definition of the package used in other classes"),
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guid("{ABBC0F60-8EA1-11d1-00A0-C90629100000}")]
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class Package {
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[WmiDataId(1), read, write, Description("16 bytes of data")] uint8 Bytes[16];
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};
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[WMI, Locale("MS\0x409"),
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Description("This class contains the definition of the package used in other classes"),
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guid("{ABBC0F63-8EA1-11d1-00A0-C90629100000}")]
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class Package_32 {
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[WmiDataId(1), read, write, Description("32 bytes of data")] uint8 Bytes[32];
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};
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[WMI, Dynamic, Provider("WmiProv"), Locale("MS\0x409"),
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Description("Class used to operate methods on a package"),
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guid("{ABBC0F6E-8EA1-11d1-00A0-C90629100000}")]
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class MSI_ACPI {
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[key, read] string InstanceName;
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[read] boolean Active;
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[WmiMethodId(1), Implemented, read, write, Description("Return the contents of a package")]
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void GetPackage([out, id(0)] Package Data);
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[WmiMethodId(2), Implemented, read, write, Description("Set the contents of a package")]
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void SetPackage([in, id(0)] Package Data);
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[WmiMethodId(3), Implemented, read, write, Description("Return the contents of a package")]
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void Get_EC([out, id(0)] Package_32 Data);
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[WmiMethodId(4), Implemented, read, write, Description("Set the contents of a package")]
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void Set_EC([in, id(0)] Package_32 Data);
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[WmiMethodId(5), Implemented, read, write, Description("Return the contents of a package")]
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void Get_BIOS([in, out, id(0)] Package_32 Data);
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[WmiMethodId(6), Implemented, read, write, Description("Set the contents of a package")]
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void Set_BIOS([in, out, id(0)] Package_32 Data);
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[WmiMethodId(7), Implemented, read, write, Description("Return the contents of a package")]
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void Get_SMBUS([in, out, id(0)] Package_32 Data);
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[WmiMethodId(8), Implemented, read, write, Description("Set the contents of a package")]
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void Set_SMBUS([in, out, id(0)] Package_32 Data);
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[WmiMethodId(9), Implemented, read, write, Description("Return the contents of a package")]
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void Get_MasterBattery([in, out, id(0)] Package_32 Data);
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[WmiMethodId(10), Implemented, read, write, Description("Set the contents of a package")]
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void Set_MasterBattery([in, out, id(0)] Package_32 Data);
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[WmiMethodId(11), Implemented, read, write, Description("Return the contents of a package")]
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void Get_SlaveBattery([in, out, id(0)] Package_32 Data);
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[WmiMethodId(12), Implemented, read, write, Description("Set the contents of a package")]
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void Set_SlaveBattery([in, out, id(0)] Package_32 Data);
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[WmiMethodId(13), Implemented, read, write, Description("Return the contents of a package")]
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void Get_Temperature([in, out, id(0)] Package_32 Data);
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[WmiMethodId(14), Implemented, read, write, Description("Set the contents of a package")]
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void Set_Temperature([in, out, id(0)] Package_32 Data);
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[WmiMethodId(15), Implemented, read, write, Description("Return the contents of a package")]
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void Get_Thermal([in, out, id(0)] Package_32 Data);
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[WmiMethodId(16), Implemented, read, write, Description("Set the contents of a package")]
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void Set_Thermal([in, out, id(0)] Package_32 Data);
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[WmiMethodId(17), Implemented, read, write, Description("Return the contents of a package")]
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void Get_Fan([in, out, id(0)] Package_32 Data);
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[WmiMethodId(18), Implemented, read, write, Description("Set the contents of a package")]
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void Set_Fan([in, out, id(0)] Package_32 Data);
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[WmiMethodId(19), Implemented, read, write, Description("Return the contents of a package")]
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void Get_Device([in, out, id(0)] Package_32 Data);
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[WmiMethodId(20), Implemented, read, write, Description("Set the contents of a package")]
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void Set_Device([in, out, id(0)] Package_32 Data);
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[WmiMethodId(21), Implemented, read, write, Description("Return the contents of a package")]
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void Get_Power([in, out, id(0)] Package_32 Data);
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[WmiMethodId(22), Implemented, read, write, Description("Set the contents of a package")]
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void Set_Power([in, out, id(0)] Package_32 Data);
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[WmiMethodId(23), Implemented, read, write, Description("Return the contents of a package")]
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void Get_Debug([in, out, id(0)] Package_32 Data);
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[WmiMethodId(24), Implemented, read, write, Description("Set the contents of a package")]
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void Set_Debug([in, out, id(0)] Package_32 Data);
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[WmiMethodId(25), Implemented, read, write, Description("Return the contents of a package")]
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void Get_AP([in, out, id(0)] Package_32 Data);
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[WmiMethodId(26), Implemented, read, write, Description("Set the contents of a package")]
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void Set_AP([in, out, id(0)] Package_32 Data);
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[WmiMethodId(27), Implemented, read, write, Description("Return the contents of a package")]
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void Get_Data([in, out, id(0)] Package_32 Data);
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[WmiMethodId(28), Implemented, read, write, Description("Set the contents of a package")]
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void Set_Data([in, out, id(0)] Package_32 Data);
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[WmiMethodId(29), Implemented, read, write, Description("Return the contents of a package")]
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void Get_WMI([out, id(0)] Package_32 Data);
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};
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Due to a peculiarity in how Windows handles the ``CreateByteField()`` ACPI operator (errors only
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happen when a invalid byte field is ultimately accessed), all methods require a 32 byte input
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2024-07-30 17:15:59 -07:00
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buffer, even if the Binary MOF says otherwise.
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The input buffer contains a single byte to select the subfeature to be accessed and 31 bytes of
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input data, the meaning of which depends on the subfeature being accessed.
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2024-07-30 17:15:59 -07:00
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The output buffer contains a single byte which signals success or failure (``0x00`` on failure)
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and 31 bytes of output data, the meaning if which depends on the subfeature being accessed.
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WMI method Get_EC()
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-------------------
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Returns embedded controller information, the selected subfeature does not matter. The output
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data contains a flag byte and a 28 byte controller firmware version string.
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The first 4 bits of the flag byte contain the minor version of the embedded controller interface,
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with the next 2 bits containing the major version of the embedded controller interface.
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2024-07-30 17:15:59 -07:00
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The 7th bit signals if the embedded controller page changed (exact meaning is unknown), and the
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last bit signals if the platform is a Tigerlake platform.
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The MSI software seems to only use this interface when the last bit is set.
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WMI method Get_Fan()
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--------------------
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Fan speed sensors can be accessed by selecting subfeature ``0x00``. The output data contains
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up to four 16-bit fan speed readings in big-endian format. Most machines do not support all
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four fan speed sensors, so the remaining reading are hardcoded to ``0x0000``.
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The fan RPM readings can be calculated with the following formula:
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RPM = 480000 / <fan speed reading>
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If the fan speed reading is zero, then the fan RPM is zero too.
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WMI method Get_WMI()
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--------------------
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Returns the version of the ACPI WMI interface, the selected subfeature does not matter.
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The output data contains two bytes, the first one contains the major version and the last one
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contains the minor revision of the ACPI WMI interface.
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The MSI software seems to only use this interface when the major version is greater than two.
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Reverse-Engineering the MSI WMI Platform interface
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==================================================
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.. warning:: Randomly poking the embedded controller interface can potentially cause damage
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to the machine and other unwanted side effects, please be careful.
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The underlying embedded controller interface is used by the ``msi-ec`` driver, and it seems
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that many methods just copy a part of the embedded controller memory into the output buffer.
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This means that the remaining WMI methods can be reverse-engineered by looking which part of
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the embedded controller memory is accessed by the ACPI AML code. The driver also supports a
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debugfs interface for directly executing WMI methods. Additionally, any safety checks regarding
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unsupported hardware can be disabled by loading the module with ``force=true``.
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More information about the MSI embedded controller interface can be found at the
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`msi-ec project <https://github.com/BeardOverflow/msi-ec>`_.
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Special thanks go to github user `glpnk` for showing how to decode the fan speed readings.
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