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coresight: docs: Add information about the topology representations

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

Signed-off-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200518180242.7916-7-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mike Leach 2020-05-18 12:02:25 -06:00 committed by Greg Kroah-Hartman
parent 73274abb65
commit 5153e57bf8
2 changed files with 89 additions and 1 deletions
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5
Documentation/trace/coresight/coresight-ect.rst
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@ -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

85
Documentation/trace/coresight/coresight.rst
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@ -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
-----------------------------