ETM can be enabled from ADB shell. However if tescase involves reboots, we make the changes in script that would keep ETM enabled after reboot. 

1) Step#1: As a first step proper build is required with coresight settings on APSS build.

These are configs required in defconfig file:

CONFIG_CORESIGHT=y
CONFIG_CORESIGHT_LINK_AND_SINK_TMC=y
CONFIG_CORESIGHT_SOURCE_ETM4X=y
CONFIG_CORESIGHT_DYNAMIC_REPLICATOR=y
CONFIG_CORESIGHT_STM=y
CONFIG_CORESIGHT_CTI=y
CONFIG_CORESIGHT_TPDA=y
CONFIG_CORESIGHT_TPDM=y
CONFIG_CORESIGHT_HWEVENT=y
CONFIG_CORESIGHT_DUMMY=y
CONFIG_CORESIGHT_REMOTE_ETM=y
CONFIG_CORESIGHT_REMOTE_ETM_DEFAULT_ENABLE=0
CONFIG_CORESIGHT_TGU=y
CONFIG_CORESIGHT_EVENT=y

2) Step #2: If device is secure boot enabled, kindly enable debug policy and use JTAG override to re-enable ETM along wth above build.

3) Step#3: Manual verification to see if modem ETM works fine:

  try to do 
     echo 1 > /sys/bus/coresight/devices/coresight-tmc-etr/enable_sink 
     echo 1 > /sys/bus/coresight/devices/coresight-modem-etm0/enable_source 

  After this check 

     cat /sys/bus/coresight/devices/coresight-tmc-etr/enable_sink 
     cat /sys/bus/coresight/devices/coresight-modem-etm0/enable_source 

  These should return value "1".
  If this step fails, then look for any failure prints in APPS DMESG or ADB shell to debug further. It would be likely a case of Debug policy and JTAG override not flashed correctly or some QMI error.
  
  
4)Then pull etm file from live device and check contents with Hex-editor to see if these are non-zero:

   adb root
   adb shell
   >>cat /dev/coresight-tmc-etr  > /data/tmc-etr.bin 
  adb pull /data/tmc-etr.bin <location to save etr bin>\tmc-etr.bin

5) Once this step is verified, it means ETM is up and can be used.


/*********************  If test involvs reboots, use the following steps to enable ETM across reboot *************************/


NOTE : Please refer   QDSS Configure ETM String Format Specification 80-NV553-1 Rev. A  for more details on usage of qdss_qmi_helper app.

1) Copy all 3 files to a local PC path, say c:\etm_enable

2) Edit etm_enable.bat to change path accordngly: "c:\etm_enable\qdss_qmi_helper"

3) run the batch file etm_enable.bat from windows command prompt. Device will automatically reboot at end of this. Observe for any failures on command prompt.

4) To verify if ETM is enabled:

cat /sys/bus/coresight/devices/coresight-tmc-etr/enable_sink

cat /sys/bus/coresight/devices/coresight-modem-etm0/enable_source

This should return value "1". If this comes as "1", we are good to go with testing to reproduce the original issue.

5) Then pull etm file from live device and check contents with Hex-editor to see if these are non-zero:

   adb root
   adb shell
   >>cat /dev/coresight-tmc-etr  > /data/tmc-etr.bin 
  adb pull /data/tmc-etr.bin <location to save etr bin>\tmc-etr.bin 

6) Please share the tmc-etr.bin file or You could also share a forced crash dump with us.