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    Subject[PATCH 2/3] coresight: Add section for integration with the perf tools
    Date
    Adding a section that document how to use the Coresight framework and
    drivers from the perf tools.

    Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
    ---
    Documentation/trace/coresight.txt | 50 +++++++++++++++++++++++++++++++++++++++
    1 file changed, 50 insertions(+)

    diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt
    index 710c75b6c73f..8caae8050a60 100644
    --- a/Documentation/trace/coresight.txt
    +++ b/Documentation/trace/coresight.txt
    @@ -187,9 +187,18 @@ that can be performed on them (see "struct coresight_ops"). The
    specific to that component only. "Implementation defined" customisations are
    expected to be accessed and controlled using those entries.

    +
    How to use the tracer modules
    -----------------------------

    +There is two ways to use the Coresight framework: 1) using the perf cmd line
    +tools and 2) interacting directly with the Coresight devices using the sysFS
    +interface. Preference is given to the former as using the sysFS interface
    +requires a deep understanding of the Coresight HW. The following sections
    +provide details on using both methods.
    +
    +1) Using the sysFS interface:
    +
    Before trace collection can start, a coresight sink needs to be identify.
    There is no limit on the amount of sinks (nor sources) that can be enabled at
    any given moment. As a generic operation, all device pertaining to the sink
    @@ -295,6 +304,47 @@ Instruction 13570831 0x8026B584 E28DD00C false ADD
    Instruction 0 0x8026B588 E8BD8000 true LDM sp!,{pc}
    Timestamp Timestamp: 17107041535

    +2) Using perf framework:
    +
    +Coresight tracers are represented using the Perf framework's Performance
    +Monitoring Unit (PMU) abstraction. As such the perf framework takes charge of
    +controlling when tracing gets enabled based on when the process of interest is
    +scheduled. When configured in a system, Coresight PMUs will be listed when
    +queried by the perf command line tool:
    +
    + linaro@linaro-nano:~$ ./perf list pmu
    +
    + List of pre-defined events (to be used in -e):
    +
    + cs_etm// [Kernel PMU event]
    +
    + linaro@linaro-nano:~$
    +
    +Regardless of the number of tracers available in a system (usually equal to the
    +amount of processor core), the "cs_etm" PMU will be listed only once.
    +
    +A Coresight PMU works the same way as any other PMUs, i.e the name of the PMU is
    +listed along with configuration options within forward slashes '/'. Since a
    +Coresight system will typically have more than one sink, the name of the sink to
    +work with needs to be specified as an event option. Names for sink to choose
    +from are listed in sysFS under ($SYSFS)/bus/coresight/devices:
    +
    + root@linaro-nano:~# ls /sys/bus/coresight/devices/
    + 20010000.etf 20040000.funnel 20100000.stm 22040000.etm
    + 22140000.etm 230c0000.funnel 23240000.etm 20030000.tpiu
    + 20070000.etr 20120000.replicator 220c0000.funnel
    + 23040000.etm 23140000.etm 23340000.etm
    +
    + root@linaro-nano:~# perf record -e cs_etm/@20070000.etr/u --per-thread program
    +
    +The syntax within the forward slashes '/' is important. The '@' character
    +tells the parser that a sink is about to be specified and that this is the IP
    +to use for the trace session.
    +
    +More information on the above and other example on how to use Coresight with
    +the perf tools can be found in the "HOWTO.md" file of the openCSD gitHub
    +repository [3].
    +
    How to use the STM module
    -------------------------

    --
    2.7.4
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