docs(amu): add AMU documentation
This change adds some documentation on the AMU and its purpose. This is
expanded on in later patches.
Change-Id: If2834676790938d8da5ea2ceba37b674f6cc0f01
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/docs/components/activity-monitors.rst b/docs/components/activity-monitors.rst
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+Activity Monitors
+=================
+
+FEAT_AMUv1 of the Armv8-A architecture introduces the Activity Monitors
+extension. This extension describes the architecture for the Activity Monitor
+Unit (|AMU|), an optional non-invasive component for monitoring core events
+through a set of 64-bit counters.
+
+When the ``ENABLE_AMU=1`` build option is provided, Trusted Firmware-A sets up
+the |AMU| prior to its exit from EL3, and will save and restore architected
+|AMU| counters as necessary upon suspend and resume.
+
+--------------
+
+*Copyright (c) 2021, Arm Limited. All rights reserved.*