Updates the CoreSight documentation to cover the use of default sinks for
both perf and sysfs operations.
Signed-off-by: Mike Leach <mike.leach@xxxxxxxxxx>
---
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]_.
--
2.17.1
