2Arm Coherent Mesh Network PMU
   5CMN-600 is a configurable mesh interconnect consisting of a rectangular
   6grid of crosspoints (XPs), with each crosspoint supporting up to two
   7device ports to which various AMBA CHI agents are attached.
   9CMN implements a distributed PMU design as part of its debug and trace
  10functionality. This consists of a local monitor (DTM) at every XP, which
  11counts up to 4 event signals from the connected device nodes and/or the
  12XP itself. Overflow from these local counters is accumulated in up to 8
  13global counters implemented by the main controller (DTC), which provides
  14overall PMU control and interrupts for global counter overflow.
  16PMU events
  19The PMU driver registers a single PMU device for the whole interconnect,
  20see /sys/bus/event_source/devices/arm_cmn_0. Multi-chip systems may link
  21more than one CMN together via external CCIX links - in this situation,
  22each mesh counts its own events entirely independently, and additional
  23PMU devices will be named arm_cmn_{1..n}.
  25Most events are specified in a format based directly on the TRM
  26definitions - "type" selects the respective node type, and "eventid" the
  27event number. Some events require an additional occupancy ID, which is
  28specified by "occupid".
  30* Since RN-D nodes do not have any distinct events from RN-I nodes, they
  31  are treated as the same type (0xa), and the common event templates are
  32  named "rnid_*".
  34* The cycle counter is treated as a synthetic event belonging to the DTC
  35  node ("type" == 0x3, "eventid" is ignored).
  37* XP events also encode the port and channel in the "eventid" field, to
  38  match the underlying pmu_event0_id encoding for the pmu_event_sel
  39  register. The event templates are named with prefixes to cover all
  40  permutations.
  42By default each event provides an aggregate count over all nodes of the
  43given type. To target a specific node, "bynodeid" must be set to 1 and
  44"nodeid" to the appropriate value derived from the CMN configuration
  45(as defined in the "Node ID Mapping" section of the TRM).
  50The PMU can also count watchpoint events to monitor specific flit
  51traffic. Watchpoints are treated as a synthetic event type, and like PMU
  52events can be global or targeted with a particular XP's "nodeid" value.
  53Since the watchpoint direction is otherwise implicit in the underlying
  54register selection, separate events are provided for flit uploads and
  57The flit match value and mask are passed in config1 and config2 ("val"
  58and "mask" respectively). "wp_dev_sel", "wp_chn_sel", "wp_grp" and
  59"wp_exclusive" are specified per the TRM definitions for dtm_wp_config0.
  60Where a watchpoint needs to match fields from both match groups on the
  61REQ or SNP channel, it can be specified as two events - one for each
  62group - with the same nonzero "combine" value. The count for such a
  63pair of combined events will be attributed to the primary match.
  64Watchpoint events with a "combine" value of 0 are considered independent
  65and will count individually.