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