feat(mpmm): add support for MPMM
MPMM - the Maximum Power Mitigation Mechanism - is an optional
microarchitectural feature present on some Armv9-A cores, introduced
with the Cortex-X2, Cortex-A710 and Cortex-A510 cores.
MPMM allows the SoC firmware to detect and limit 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.
This feature is enabled via the `ENABLE_MPMM` build option.
Configuration can be done via FCONF by enabling `ENABLE_MPMM_FCONF`, or
by via the plaform-implemented `plat_mpmm_topology` function.
Change-Id: I77da82808ad4744ece8263f0bf215c5a091c3167
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/docs/components/mpmm.rst b/docs/components/mpmm.rst
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+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 ``ENABLE_MPMM_FCONF`` build option.
+- A platform implementation of the ``plat_mpmm_topology`` function (the
+ default).
+
+See :ref:`Maximum Power Mitigation Mechanism (MPMM) Bindings` for documentation
+on the |FCONF| device tree bindings.
+
+.. warning::
+
+ |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 :ref:`Activity Monitor Auxiliary Counters` for
+ documentation on enabling auxiliary |AMU| counters.