66 lines
3.0 KiB
ReStructuredText
66 lines
3.0 KiB
ReStructuredText
=============================
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Arm Coherent Mesh Network PMU
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=============================
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CMN-600 is a configurable mesh interconnect consisting of a rectangular
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grid of crosspoints (XPs), with each crosspoint supporting up to two
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device ports to which various AMBA CHI agents are attached.
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CMN implements a distributed PMU design as part of its debug and trace
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functionality. This consists of a local monitor (DTM) at every XP, which
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counts up to 4 event signals from the connected device nodes and/or the
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XP itself. Overflow from these local counters is accumulated in up to 8
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global counters implemented by the main controller (DTC), which provides
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overall PMU control and interrupts for global counter overflow.
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PMU events
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----------
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The PMU driver registers a single PMU device for the whole interconnect,
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see /sys/bus/event_source/devices/arm_cmn_0. Multi-chip systems may link
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more than one CMN together via external CCIX links - in this situation,
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each mesh counts its own events entirely independently, and additional
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PMU devices will be named arm_cmn_{1..n}.
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Most events are specified in a format based directly on the TRM
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definitions - "type" selects the respective node type, and "eventid" the
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event number. Some events require an additional occupancy ID, which is
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specified by "occupid".
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* Since RN-D nodes do not have any distinct events from RN-I nodes, they
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are treated as the same type (0xa), and the common event templates are
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named "rnid_*".
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* The cycle counter is treated as a synthetic event belonging to the DTC
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node ("type" == 0x3, "eventid" is ignored).
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* XP events also encode the port and channel in the "eventid" field, to
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match the underlying pmu_event0_id encoding for the pmu_event_sel
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register. The event templates are named with prefixes to cover all
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permutations.
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By default each event provides an aggregate count over all nodes of the
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given type. To target a specific node, "bynodeid" must be set to 1 and
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"nodeid" to the appropriate value derived from the CMN configuration
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(as defined in the "Node ID Mapping" section of the TRM).
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Watchpoints
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-----------
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The PMU can also count watchpoint events to monitor specific flit
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traffic. Watchpoints are treated as a synthetic event type, and like PMU
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events can be global or targeted with a particular XP's "nodeid" value.
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Since the watchpoint direction is otherwise implicit in the underlying
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register selection, separate events are provided for flit uploads and
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downloads.
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The flit match value and mask are passed in config1 and config2 ("val"
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and "mask" respectively). "wp_dev_sel", "wp_chn_sel", "wp_grp" and
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"wp_exclusive" are specified per the TRM definitions for dtm_wp_config0.
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Where a watchpoint needs to match fields from both match groups on the
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REQ or SNP channel, it can be specified as two events - one for each
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group - with the same nonzero "combine" value. The count for such a
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pair of combined events will be attributed to the primary match.
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Watchpoint events with a "combine" value of 0 are considered independent
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and will count individually.
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