1 =============================
2 Arm Coherent Mesh Network PMU
3 =============================
4
5 CMN-600 is a configurable mesh interconnect consisting of a rectangular
6 grid of crosspoints (XPs), with each crosspoint supporting up to two
7 device ports to which various AMBA CHI agents are attached.
8
9 CMN implements a distributed PMU design as part of its debug and trace
10 functionality. This consists of a local monitor (DTM) at every XP, which
11 counts up to 4 event signals from the connected device nodes and/or the
12 XP itself. Overflow from these local counters is accumulated in up to 8
13 global counters implemented by the main controller (DTC), which provides
14 overall PMU control and interrupts for global counter overflow.
15
16 PMU events
17 ----------
18
19 The PMU driver registers a single PMU device for the whole interconnect,
20 see /sys/bus/event_source/devices/arm_cmn_0. Multi-chip systems may link
21 more than one CMN together via external CCIX links - in this situation,
22 each mesh counts its own events entirely independently, and additional
23 PMU devices will be named arm_cmn_{1..n}.
24
25 Most events are specified in a format based directly on the TRM
26 definitions - "type" selects the respective node type, and "eventid" the
27 event number. Some events require an additional occupancy ID, which is
28 specified by "occupid".
29
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_*".
33
34 * The cycle counter is treated as a synthetic event belonging to the DTC
35 node ("type" == 0x3, "eventid" is ignored).
36
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.
41
42 By default each event provides an aggregate count over all nodes of the
43 given 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).
46
47 Watchpoints
48 -----------
49
50 The PMU can also count watchpoint events to monitor specific flit
51 traffic. Watchpoints are treated as a synthetic event type, and like PMU
52 events can be global or targeted with a particular XP's "nodeid" value.
53 Since the watchpoint direction is otherwise implicit in the underlying
54 register selection, separate events are provided for flit uploads and
55 downloads.
56
57 The flit match value and mask are passed in config1 and config2 ("val"
58 and "mask" respectively). "wp_dev_sel", "wp_chn_sel", "wp_grp" and
59 "wp_exclusive" are specified per the TRM definitions for dtm_wp_config0.
60 Where a watchpoint needs to match fields from both match groups on the
61 REQ or SNP channel, it can be specified as two events - one for each
62 group - with the same nonzero "combine" value. The count for such a
63 pair of combined events will be attributed to the primary match.
64 Watchpoint events with a "combine" value of 0 are considered independent
65 and will count individually.
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