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Windows Kernel-Mode Platform Runtime Mechanism (PRM) Library

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The Platform Runtime Mechanism (PRM) is a GUID-based interface that enables drivers to run handlers preloaded in Unified Extensible Firmware Interface (UEFI) firmware. PRM offers functionality similar to System Management Interrupt (SMI) calls in System Management Mode (SMM), but it's more secure.

During system runtime, the firmware may contain several PRM modules, each with a unique set of handlers.

Drivers can call PRM handlers for low-level operations such as controlling hardware components, managing thermal states, or advanced power management.

Follow these steps to check for the availability of a specific handler and to run it. You can find a sample implementation of this process in the PrmFunc sample.

  1. Obtain a pointer to a PRM_INTERFACE structure by calling the ExGetPrmInterface routine. This structure contains pointers to the PRM operation routines.

  2. Synchronize against potential runtime updates to the PRM module by calling the PRM_LOCK_MODULE routine. Lock and unlock calls are necessary for transactional series of PRM handler calls, but it's generally recommended to use them.

  3. Check the presence of the specified PRM handler using the PRM_QUERY_HANDLER routine.

  4. If the query succeeds, invoke the PRM handler by calling the PRM_INVOKE_HANDLER routine. Provide the GUID and the parameter buffer, which should contain the parameters for the PRM handler. The EfiStatus output parameter will indicate the status of the handler invocation.

  5. If you previously called PRM_LOCK_MODULE, release the PRM interface object by calling the PRM_UNLOCK_MODULE routine.

See also

For more information, refer to the PRM specification.