tracing: Document trace_marker triggers

Add documentation and an example on how to use trace_marker triggers.

Reviewed-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 67d9c38e95eb..aad4776c0f5d 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -507,6 +507,11 @@ of ftrace. Here is a list of some of the key files:
 
 		trace_fd = open("trace_marker", WR_ONLY);
 
+	Note: Writing into the trace_marker file can also initiate triggers
+	      that are written into /sys/kernel/tracing/events/ftrace/print/trigger
+	      See "Event triggers" in Documentation/trace/events.rst and an
+              example in Documentation/trace/histogram.rst (Section 3.)
+
   trace_marker_raw:
 
 	This is similar to trace_marker above, but is meant for for binary data