66 lines
3.0 KiB
ReStructuredText
66 lines
3.0 KiB
ReStructuredText
|
=============================
|
||
|
|
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.
|