1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 =================== 3 ===================
4 MIPI SyS-T over STP 4 MIPI SyS-T over STP
5 =================== 5 ===================
6 6
7 The MIPI SyS-T protocol driver can be used wit 7 The MIPI SyS-T protocol driver can be used with STM class devices to
8 generate standardized trace stream. Aside from 8 generate standardized trace stream. Aside from being a standard, it
9 provides better trace source identification an 9 provides better trace source identification and timestamp correlation.
10 10
11 In order to use the MIPI SyS-T protocol driver 11 In order to use the MIPI SyS-T protocol driver with your STM device,
12 first, you'll need CONFIG_STM_PROTO_SYS_T. 12 first, you'll need CONFIG_STM_PROTO_SYS_T.
13 13
14 Now, you can select which protocol driver you 14 Now, you can select which protocol driver you want to use when you create
15 a policy for your STM device, by specifying it 15 a policy for your STM device, by specifying it in the policy name:
16 16
17 # mkdir /config/stp-policy/dummy_stm.0:p_sys-t 17 # mkdir /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/
18 18
19 In other words, the policy name format is exte 19 In other words, the policy name format is extended like this:
20 20
21 <device_name>:<protocol_name>.<policy_name> 21 <device_name>:<protocol_name>.<policy_name>
22 22
23 With Intel TH, therefore it can look like "0-s 23 With Intel TH, therefore it can look like "0-sth:p_sys-t.my-policy".
24 24
25 If the protocol name is omitted, the STM class 25 If the protocol name is omitted, the STM class will chose whichever
26 protocol driver was loaded first. 26 protocol driver was loaded first.
27 27
28 You can also double check that everything is w 28 You can also double check that everything is working as expected by
29 29
30 # cat /config/stp-policy/dummy_stm.0:p_sys-t.m 30 # cat /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/protocol
31 p_sys-t 31 p_sys-t
32 32
33 Now, with the MIPI SyS-T protocol driver, each 33 Now, with the MIPI SyS-T protocol driver, each policy node in the
34 configfs gets a few additional attributes, whi 34 configfs gets a few additional attributes, which determine per-source
35 parameters specific to the protocol: 35 parameters specific to the protocol:
36 36
37 # mkdir /config/stp-policy/dummy_stm.0:p_sys-t 37 # mkdir /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/default
38 # ls /config/stp-policy/dummy_stm.0:p_sys-t.my 38 # ls /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/default
39 channels 39 channels
40 clocksync_interval 40 clocksync_interval
41 do_len 41 do_len
42 masters 42 masters
43 ts_interval 43 ts_interval
44 uuid 44 uuid
45 45
46 The most important one here is the "uuid", whi 46 The most important one here is the "uuid", which determines the UUID
47 that will be used to tag all data coming from 47 that will be used to tag all data coming from this source. It is
48 automatically generated when a new node is cre 48 automatically generated when a new node is created, but it is likely
49 that you would want to change it. 49 that you would want to change it.
50 50
51 do_len switches on/off the additional "payload 51 do_len switches on/off the additional "payload length" field in the
52 MIPI SyS-T message header. It is off by defaul 52 MIPI SyS-T message header. It is off by default as the STP already
53 marks message boundaries. 53 marks message boundaries.
54 54
55 ts_interval and clocksync_interval determine h 55 ts_interval and clocksync_interval determine how much time in milliseconds
56 can pass before we need to include a protocol 56 can pass before we need to include a protocol (not transport, aka STP)
57 timestamp in a message header or send a CLOCKS 57 timestamp in a message header or send a CLOCKSYNC packet, respectively.
58 58
59 See Documentation/ABI/testing/configfs-stp-pol 59 See Documentation/ABI/testing/configfs-stp-policy-p_sys-t for more
60 details. 60 details.
61 61
62 * [1] https://www.mipi.org/specifications/sys- 62 * [1] https://www.mipi.org/specifications/sys-t
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