Updates the CoreSight documentation to cover the use of default sinks for both perf and sysfs operations.
Signed-off-by: Mike Leach mike.leach@linaro.org --- Documentation/trace/coresight/coresight.rst | 48 +++++++++++++++------ 1 file changed, 34 insertions(+), 14 deletions(-)
diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst index 0b73acb44efa..917d89f74c2e 100644 --- a/Documentation/trace/coresight/coresight.rst +++ b/Documentation/trace/coresight/coresight.rst @@ -341,17 +341,18 @@ provide details on using both methods. 1) Using the sysFS interface:
Before trace collection can start, a coresight sink needs to be identified. -There is no limit on the amount of sinks (nor sources) that can be enabled at -any given moment. As a generic operation, all device pertaining to the sink -class will have an "active" entry in sysfs:: +There is no limit on the amount of sources and sinks that can be enabled at +any given moment. However, any source will only trace into a single sink. +As a generic operation, all device pertaining to the sink class will have an +"active" entry in sysfs::
root:/sys/bus/coresight/devices# ls - replicator 20030000.tpiu 2201c000.ptm 2203c000.etm 2203e000.etm - 20010000.etb 20040000.funnel 2201d000.ptm 2203d000.etm - root:/sys/bus/coresight/devices# ls 20010000.etb + replicator0 tpiu0 ptm0 etm2 etm3 + etb0 funnel0 ptm1 etm4 + root:/sys/bus/coresight/devices# ls etb0 enable_sink status trigger_cntr - root:/sys/bus/coresight/devices# echo 1 > 20010000.etb/enable_sink - root:/sys/bus/coresight/devices# cat 20010000.etb/enable_sink + root:/sys/bus/coresight/devices# echo 1 > etb0/enable_sink + root:/sys/bus/coresight/devices# cat etb0/enable_sink 1 root:/sys/bus/coresight/devices#
@@ -360,10 +361,10 @@ comparator with "_stext" and "_etext", essentially tracing any instruction that falls within that range. As such "enabling" a source will immediately trigger a trace capture::
- root:/sys/bus/coresight/devices# echo 1 > 2201c000.ptm/enable_source - root:/sys/bus/coresight/devices# cat 2201c000.ptm/enable_source + root:/sys/bus/coresight/devices# echo 1 > ptm0/enable_source + root:/sys/bus/coresight/devices# cat ptm0/enable_source 1 - root:/sys/bus/coresight/devices# cat 20010000.etb/status + root:/sys/bus/coresight/devices# cat etb0/status Depth: 0x2000 Status: 0x1 RAM read ptr: 0x0 @@ -376,13 +377,22 @@ trigger a trace capture::
Trace collection is stopped the same way::
- root:/sys/bus/coresight/devices# echo 0 > 2201c000.ptm/enable_source + root:/sys/bus/coresight/devices# echo 0 > ptm0/enable_source root:/sys/bus/coresight/devices#
+If no sink is enabled before the source is enabled, then a default sink will +be selected and enabled automatically. Once the source is disabled, then the +sink used can be read from <source>/last_sink.:: + + root:/sys/bus/coresight/devices# echo 1 > ptm0/enable_source + root:/sys/bus/coresight/devices# echo 0 > ptm0/enable_source + root:/sys/bus/coresight/devices# cat ptm0/last_sink + etb0 + root:/sys/bus/coresight/devices# echo 0 > etb0/enable_sink + The content of the ETB buffer can be harvested directly from /dev::
- root:/sys/bus/coresight/devices# dd if=/dev/20010000.etb \ - of=~/cstrace.bin + root:/sys/bus/coresight/devices# dd if=/dev/etb0 of=~/cstrace.bin 64+0 records in 64+0 records out 32768 bytes (33 kB) copied, 0.00125258 s, 26.2 MB/s @@ -490,6 +500,16 @@ The syntax within the forward slashes '/' is important. The '@' character tells the parser that a sink is about to be specified and that this is the sink to use for the trace session.
+Alternatively, if no sink name is given between the //, then the CoreSight +system will select a default sink:: + + root@linaro-nano:~# perf record -e cs_etm//u --per-thread program + +The system selects a sink by searching connection path from the source ETM to +any sink that is on the path.The system will prefer ETR devices over ETB/ETF, +and where two of the same type are found, the closest to the ETM, in terms of +connection links. + More information on the above and other example on how to use Coresight with the perf tools can be found in the "HOWTO.md" file of the openCSD gitHub repository [#third]_.