Commit 5153e57b authored by Mike Leach's avatar Mike Leach Committed by Greg Kroah-Hartman
Browse files

coresight: docs: Add information about the topology representations 



Update the CoreSight documents to describe the new connections directory
and the links between CoreSight devices in this directory.

Signed-off-by: default avatarMike Leach <mike.leach@linaro.org>
Signed-off-by: default avatarMathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200518180242.7916-7-mathieu.poirier@linaro.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 73274abb

Documentation/trace/coresight/coresight-ect.rst

+4 −1
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ capable of generating or using trigger signals.:: 


  >$ ls /sys/bus/coresight/devices/etm0/cti_cpu0

  channels  ctmid  enable  nr_trigger_cons mgmt  power powered  regs

  subsystem triggers0 triggers1  uevent

  connections subsystem triggers0 triggers1  uevent



*Key file items are:-*

   * ``enable``: enables/disables the CTI. Read to determine current state.
@@ -88,6 +88,9 @@ capable of generating or using trigger signals.:: 
   * ``channels``: Contains the channel API - CTI main programming interface.

   * ``regs``: Gives access to the raw programmable CTI regs.

   * ``mgmt``: the standard CoreSight management registers.

   * ``connections``: Links to connected *CoreSight* devices. The number of

     links can be 0 to ``nr_trigger_cons``. Actual number given by ``nr_links``

     in this directory.





triggers<N> directories

Documentation/trace/coresight/coresight.rst

+85 −0
Original line number Diff line number Diff line
@@ -241,6 +241,91 @@ to the newer scheme, to give a confirmation that what you see on your 
system is not unexpected. One must use the "names" as they appear on

the system under specified locations.



Topology Representation

-----------------------



Each CoreSight component has a ``connections`` directory which will contain

links to other CoreSight components. This allows the user to explore the trace

topology and for larger systems, determine the most appropriate sink for a

given source. The connection information can also be used to establish

which CTI devices are connected to a given component. This directory contains a

``nr_links`` attribute detailing the number of links in the directory.



For an ETM source, in this case ``etm0`` on a Juno platform, a typical

arrangement will be::



  linaro-developer:~# ls - l /sys/bus/coresight/devices/etm0/connections

  <file details>  cti_cpu0 -> ../../../23020000.cti/cti_cpu0

  <file details>  nr_links

  <file details>  out:0 -> ../../../230c0000.funnel/funnel2



Following the out port to ``funnel2``::



  linaro-developer:~# ls -l /sys/bus/coresight/devices/funnel2/connections

  <file details> in:0 -> ../../../23040000.etm/etm0

  <file details> in:1 -> ../../../23140000.etm/etm3

  <file details> in:2 -> ../../../23240000.etm/etm4

  <file details> in:3 -> ../../../23340000.etm/etm5

  <file details> nr_links

  <file details> out:0 -> ../../../20040000.funnel/funnel0



And again to ``funnel0``::



  linaro-developer:~# ls -l /sys/bus/coresight/devices/funnel0/connections

  <file details> in:0 -> ../../../220c0000.funnel/funnel1

  <file details> in:1 -> ../../../230c0000.funnel/funnel2

  <file details> nr_links

  <file details> out:0 -> ../../../20010000.etf/tmc_etf0



Finding the first sink ``tmc_etf0``. This can be used to collect data

as a sink, or as a link to propagate further along the chain::



  linaro-developer:~# ls -l /sys/bus/coresight/devices/tmc_etf0/connections

  <file details> cti_sys0 -> ../../../20020000.cti/cti_sys0

  <file details> in:0 -> ../../../20040000.funnel/funnel0

  <file details> nr_links

  <file details> out:0 -> ../../../20150000.funnel/funnel4



via ``funnel4``::



  linaro-developer:~# ls -l /sys/bus/coresight/devices/funnel4/connections

  <file details> in:0 -> ../../../20010000.etf/tmc_etf0

  <file details> in:1 -> ../../../20140000.etf/tmc_etf1

  <file details> nr_links

  <file details> out:0 -> ../../../20120000.replicator/replicator0



and a ``replicator0``::



  linaro-developer:~# ls -l /sys/bus/coresight/devices/replicator0/connections

  <file details> in:0 -> ../../../20150000.funnel/funnel4

  <file details> nr_links

  <file details> out:0 -> ../../../20030000.tpiu/tpiu0

  <file details> out:1 -> ../../../20070000.etr/tmc_etr0



Arriving at the final sink in the chain, ``tmc_etr0``::



  linaro-developer:~# ls -l /sys/bus/coresight/devices/tmc_etr0/connections

  <file details> cti_sys0 -> ../../../20020000.cti/cti_sys0

  <file details> in:0 -> ../../../20120000.replicator/replicator0

  <file details> nr_links



As described below, when using sysfs it is sufficient to enable a sink and

a source for successful trace. The framework will correctly enable all

intermediate links as required.



Note: ``cti_sys0`` appears in two of the connections lists above.

CTIs can connect to multiple devices and are arranged in a star topology

via the CTM. See (:doc:`coresight-ect`) [#fourth]_ for further details.

Looking at this device we see 4 connections::



  linaro-developer:~# ls -l /sys/bus/coresight/devices/cti_sys0/connections

  <file details> nr_links

  <file details> stm0 -> ../../../20100000.stm/stm0

  <file details> tmc_etf0 -> ../../../20010000.etf/tmc_etf0

  <file details> tmc_etr0 -> ../../../20070000.etr/tmc_etr0

  <file details> tpiu0 -> ../../../20030000.tpiu/tpiu0





How to use the tracer modules

-----------------------------

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