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Subject[QUEUED v20180920 11/16] stm class: Document the MIPI SyS-T protocol usage
Add a document describing MIPI SyS-T protocol driver usage.

Signed-off-by: Alexander Shishkin <>
Documentation/trace/sys-t.rst | 62 +++++++++++++++++++++++++++++++++++
1 file changed, 62 insertions(+)
create mode 100644 Documentation/trace/sys-t.rst

diff --git a/Documentation/trace/sys-t.rst b/Documentation/trace/sys-t.rst
new file mode 100644
index 000000000000..3d8eb92735e9
--- /dev/null
+++ b/Documentation/trace/sys-t.rst
@@ -0,0 +1,62 @@
+.. SPDX-License-Identifier: GPL-2.0
+MIPI SyS-T over STP
+The MIPI SyS-T protocol driver can be used with STM class devices to
+generate standardized trace stream. Aside from being a standard, it
+provides better trace source identification and timestamp correlation.
+In order to use the MIPI SyS-T protocol driver with your STM device,
+first, you'll need CONFIG_STM_PROTO_SYS_T.
+Now, you can select which protocol driver you want to use when you create
+a policy for your STM device, by specifying it in the policy name:
+# mkdir /config/stp-policy/
+In other words, the policy name format is extended like this:
+ <device_name>:<protocol_name>.<policy_name>
+With Intel TH, therefore it can look like "".
+If the protocol name is omitted, the STM class will chose whichever
+protocol driver was loaded first.
+You can also double check that everything is working as expected by
+# cat /config/stp-policy/
+Now, with the MIPI SyS-T protocol driver, each policy node in the
+configfs gets a few additional attributes, which determine per-source
+parameters specific to the protocol:
+# mkdir /config/stp-policy/
+# ls /config/stp-policy/
+The most important one here is the "uuid", which determines the UUID
+that will be used to tag all data coming from this source. It is
+automatically generated when a new node is created, but it is likely
+that you would want to change it.
+do_len switches on/off the additional "payload length" field in the
+MIPI SyS-T message header. It is off by default as the STP already
+marks message boundaries.
+ts_interval and clocksync_interval determine how much time in milliseconds
+can pass before we need to include a protocol (not transport, aka STP)
+timestamp in a message header or send a CLOCKSYNC packet, respectively.
+See Documentation/ABI/testing/configfs-stp-policy-p_sys-t for more
+* [1]
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