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Diffstat (limited to 'Documentation/hwmon/dell-smm-hwmon.rst')
| -rw-r--r-- | Documentation/hwmon/dell-smm-hwmon.rst | 38 |
1 files changed, 35 insertions, 3 deletions
diff --git a/Documentation/hwmon/dell-smm-hwmon.rst b/Documentation/hwmon/dell-smm-hwmon.rst index d8f1d6859b..977263cb57 100644 --- a/Documentation/hwmon/dell-smm-hwmon.rst +++ b/Documentation/hwmon/dell-smm-hwmon.rst @@ -186,8 +186,7 @@ SMM Interface The driver uses the SMM interface to send commands to the system BIOS. This interface is normally used by Dell's 32-bit diagnostic program or on newer notebook models by the buildin BIOS diagnostics. -The SMM is triggered by writing to the special ioports ``0xb2`` and ``0x84``, -and may cause short hangs when the BIOS code is taking too long to +The SMM may cause short hangs when the BIOS code is taking too long to execute. The SMM handler inside the system BIOS looks at the contents of the @@ -210,7 +209,40 @@ The SMM handler can signal a failure by either: - setting the lower sixteen bits of ``eax`` to ``0xffff`` - not modifying ``eax`` at all -- setting the carry flag +- setting the carry flag (legacy SMM interface only) + +Legacy SMM Interface +-------------------- + +When using the legacy SMM interface, a SMM is triggered by writing the least significant byte +of the command code to the special ioports ``0xb2`` and ``0x84``. This interface is not +described inside the ACPI tables and can thus only be detected by issuing a test SMM call. + +WMI SMM Interface +----------------- + +On modern Dell machines, the SMM calls are done over ACPI WMI: + +:: + + #pragma namespace("\\\\.\\root\\dcim\\sysman\\diagnostics") + [WMI, Provider("Provider_DiagnosticsServices"), Dynamic, Locale("MS\\0x409"), + Description("RunDellDiag"), guid("{F1DDEE52-063C-4784-A11E-8A06684B9B01}")] + class LegacyDiags { + [key, read] string InstanceName; + [read] boolean Active; + + [WmiMethodId(1), Implemented, read, write, Description("Legacy Method ")] + void Execute([in, out] uint32 EaxLen, [in, out, WmiSizeIs("EaxLen") : ToInstance] uint8 EaxVal[], + [in, out] uint32 EbxLen, [in, out, WmiSizeIs("EbxLen") : ToInstance] uint8 EbxVal[], + [in, out] uint32 EcxLen, [in, out, WmiSizeIs("EcxLen") : ToInstance] uint8 EcxVal[], + [in, out] uint32 EdxLen, [in, out, WmiSizeIs("EdxLen") : ToInstance] uint8 EdxVal[]); + }; + +Some machines support only the WMI SMM interface, while some machines support both interfaces. +The driver automatically detects which interfaces are present and will use the WMI SMM interface +if the legacy SMM interface is not present. The WMI SMM interface is usually slower than the +legacy SMM interface since ACPI methods need to be called in order to trigger a SMM. SMM command codes ----------------- |