1*4882a593Smuzhiyun.. SPDX-License-Identifier: GPL-2.0 2*4882a593Smuzhiyun 3*4882a593Smuzhiyun=================== 4*4882a593SmuzhiyunMIPI SyS-T over STP 5*4882a593Smuzhiyun=================== 6*4882a593Smuzhiyun 7*4882a593SmuzhiyunThe MIPI SyS-T protocol driver can be used with STM class devices to 8*4882a593Smuzhiyungenerate standardized trace stream. Aside from being a standard, it 9*4882a593Smuzhiyunprovides better trace source identification and timestamp correlation. 10*4882a593Smuzhiyun 11*4882a593SmuzhiyunIn order to use the MIPI SyS-T protocol driver with your STM device, 12*4882a593Smuzhiyunfirst, you'll need CONFIG_STM_PROTO_SYS_T. 13*4882a593Smuzhiyun 14*4882a593SmuzhiyunNow, you can select which protocol driver you want to use when you create 15*4882a593Smuzhiyuna policy for your STM device, by specifying it in the policy name: 16*4882a593Smuzhiyun 17*4882a593Smuzhiyun# mkdir /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/ 18*4882a593Smuzhiyun 19*4882a593SmuzhiyunIn other words, the policy name format is extended like this: 20*4882a593Smuzhiyun 21*4882a593Smuzhiyun <device_name>:<protocol_name>.<policy_name> 22*4882a593Smuzhiyun 23*4882a593SmuzhiyunWith Intel TH, therefore it can look like "0-sth:p_sys-t.my-policy". 24*4882a593Smuzhiyun 25*4882a593SmuzhiyunIf the protocol name is omitted, the STM class will chose whichever 26*4882a593Smuzhiyunprotocol driver was loaded first. 27*4882a593Smuzhiyun 28*4882a593SmuzhiyunYou can also double check that everything is working as expected by 29*4882a593Smuzhiyun 30*4882a593Smuzhiyun# cat /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/protocol 31*4882a593Smuzhiyunp_sys-t 32*4882a593Smuzhiyun 33*4882a593SmuzhiyunNow, with the MIPI SyS-T protocol driver, each policy node in the 34*4882a593Smuzhiyunconfigfs gets a few additional attributes, which determine per-source 35*4882a593Smuzhiyunparameters specific to the protocol: 36*4882a593Smuzhiyun 37*4882a593Smuzhiyun# mkdir /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/default 38*4882a593Smuzhiyun# ls /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/default 39*4882a593Smuzhiyunchannels 40*4882a593Smuzhiyunclocksync_interval 41*4882a593Smuzhiyundo_len 42*4882a593Smuzhiyunmasters 43*4882a593Smuzhiyunts_interval 44*4882a593Smuzhiyunuuid 45*4882a593Smuzhiyun 46*4882a593SmuzhiyunThe most important one here is the "uuid", which determines the UUID 47*4882a593Smuzhiyunthat will be used to tag all data coming from this source. It is 48*4882a593Smuzhiyunautomatically generated when a new node is created, but it is likely 49*4882a593Smuzhiyunthat you would want to change it. 50*4882a593Smuzhiyun 51*4882a593Smuzhiyundo_len switches on/off the additional "payload length" field in the 52*4882a593SmuzhiyunMIPI SyS-T message header. It is off by default as the STP already 53*4882a593Smuzhiyunmarks message boundaries. 54*4882a593Smuzhiyun 55*4882a593Smuzhiyunts_interval and clocksync_interval determine how much time in milliseconds 56*4882a593Smuzhiyuncan pass before we need to include a protocol (not transport, aka STP) 57*4882a593Smuzhiyuntimestamp in a message header or send a CLOCKSYNC packet, respectively. 58*4882a593Smuzhiyun 59*4882a593SmuzhiyunSee Documentation/ABI/testing/configfs-stp-policy-p_sys-t for more 60*4882a593Smuzhiyundetails. 61*4882a593Smuzhiyun 62*4882a593Smuzhiyun* [1] https://www.mipi.org/specifications/sys-t 63