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author | Alexander Shishkin <alexander.shishkin@linux.intel.com> | 2018-10-05 15:43:01 +0300 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-10-11 12:12:55 +0200 |
commit | 4cb3653df0cd0214798dc79fc13db026fbc8aa39 (patch) | |
tree | 8ad3a7df8335e71f156e28a81b599f813578ebf7 /Documentation/trace | |
parent | 95323943b791617c892738e8d2762c6661bd4382 (diff) | |
download | linux-4cb3653df0cd0214798dc79fc13db026fbc8aa39.tar.bz2 |
stm class: Document the MIPI SyS-T protocol usage
Add a document describing MIPI SyS-T protocol driver usage.
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/trace')
-rw-r--r-- | Documentation/trace/sys-t.rst | 62 |
1 files changed, 62 insertions, 0 deletions
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/dummy_stm.0:p_sys-t.my-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 "0-sth:p_sys-t.my-policy". + +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/dummy_stm.0:p_sys-t.my-policy/protocol +p_sys-t + +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/dummy_stm.0:p_sys-t.my-policy/default +# ls /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/default +channels +clocksync_interval +do_len +masters +ts_interval +uuid + +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 +details. + +* [1] https://www.mipi.org/specifications/sys-t |