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+ARM Cache Coherent Network
+==========================
+
+CCN-504 is a ring-bus interconnect consisting of 11 crosspoints
+(XPs), with each crosspoint supporting up to two device ports,
+so nodes (devices) 0 and 1 are connected to crosspoint 0,
+nodes 2 and 3 to crosspoint 1 etc.
+
+PMU (perf) driver
+-----------------
+
+The CCN driver registers a perf PMU driver, which provides
+description of available events and configuration options
+in sysfs, see /sys/bus/event_source/devices/ccn*.
+
+The "format" directory describes format of the config, config1
+and config2 fields of the perf_event_attr structure. The "events"
+directory provides configuration templates for all documented
+events, that can be used with perf tool. For example "xp_valid_flit"
+is an equivalent of "type=0x8,event=0x4". Other parameters must be
+explicitly specified. For events originating from device, "node"
+defines its index. All crosspoint events require "xp" (index),
+"port" (device port number) and "vc" (virtual channel ID) and
+"dir" (direction). Watchpoints (special "event" value 0xfe) also
+require comparator values ("cmp_l" and "cmp_h") and "mask", being
+index of the comparator mask.
+
+Masks are defined separately from the event description
+(due to limited number of the config values) in the "cmp_mask"
+directory, with first 8 configurable by user and additional
+4 hardcoded for the most frequent use cases.
+
+Cycle counter is described by a "type" value 0xff and does
+not require any other settings.
+
+Example of perf tool use:
+
+/ # perf list | grep ccn
+  ccn/cycles/                                        [Kernel PMU event]
+<...>
+  ccn/xp_valid_flit/                                 [Kernel PMU event]
+<...>
+
+/ # perf stat -C 0 -e ccn/cycles/,ccn/xp_valid_flit,xp=1,port=0,vc=1,dir=1/ \
+                                                                       sleep 1
+
+The driver does not support sampling, therefore "perf record" will
+not work. Also notice that only single cpu is being selected
+("-C 0") - this is because perf framework does not support
+"non-CPU related" counters (yet?) so system-wide session ("-a")
+would try (and in most cases fail) to set up the same event
+per each CPU.