63 строки
2.1 KiB
ReStructuredText
63 строки
2.1 KiB
ReStructuredText
.. 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
|