9. Maximum Power Mitigation Mechanism (MPMM)
MPMM is an optional microarchitectural power management mechanism supported by some Arm Armv9-A cores, beginning with the Cortex-X2, Cortex-A710 and Cortex-A510 cores. This mechanism detects and limits high-activity events to assist in SoC processor power domain dynamic power budgeting and limit the triggering of whole-rail (i.e. clock chopping) responses to overcurrent conditions.
MPMM is enabled on a per-core basis by the EL3 runtime firmware. The presence of MPMM cannot be determined at runtime by the firmware, and therefore the platform must expose this information through one of two possible mechanisms:
FCONF, controlled by the
A platform implementation of the
plat_mpmm_topologyfunction (the default).
See Maximum Power Mitigation Mechanism (MPMM) Bindings for documentation on the FCONF device tree bindings.
MPMM exposes gear metrics through the auxiliary AMU counters. An external power controller can use these metrics to budget SoC power by limiting the number of cores that can execute higher-activity workloads or switching to a different DVFS operating point. When this is the case, the AMU counters that make up the MPMM gears must be enabled by the EL3 runtime firmware - please see Auxiliary counters for documentation on enabling auxiliary AMU counters.