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