Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+======================================
+Coresight - HW Assisted Tracing on ARM
+======================================
+
+   :Author:   Mathieu Poirier <mathieu.poirier@linaro.org>
+   :Date:     September 11th, 2014
+
+Introduction
+------------
+
+Coresight is an umbrella of technologies allowing for the debugging of ARM
+based SoC.  It includes solutions for JTAG and HW assisted tracing.  This
+document is concerned with the latter.
+
+HW assisted tracing is becoming increasingly useful when dealing with systems
+that have many SoCs and other components like GPU and DMA engines.  ARM has
+developed a HW assisted tracing solution by means of different components, each
+being added to a design at synthesis time to cater to specific tracing needs.
+Components are generally categorised as source, link and sinks and are
+(usually) discovered using the AMBA bus.
+
+"Sources" generate a compressed stream representing the processor instruction
+path based on tracing scenarios as configured by users.  From there the stream
+flows through the coresight system (via ATB bus) using links that are connecting
+the emanating source to a sink(s).  Sinks serve as endpoints to the coresight
+implementation, either storing the compressed stream in a memory buffer or
+creating an interface to the outside world where data can be transferred to a
+host without fear of filling up the onboard coresight memory buffer.
+
+At typical coresight system would look like this::
+
+  *****************************************************************
+ **************************** AMBA AXI  ****************************===||
+  *****************************************************************    ||
+        ^                    ^                            |            ||
+        |                    |                            *            **
+     0000000    :::::     0000000    :::::    :::::    @@@@@@@    ||||||||||||
+     0 CPU 0<-->: C :     0 CPU 0<-->: C :    : C :    @ STM @    || System ||
+  |->0000000    : T :  |->0000000    : T :    : T :<--->@@@@@     || Memory ||
+  |  #######<-->: I :  |  #######<-->: I :    : I :      @@@<-|   ||||||||||||
+  |  # ETM #    :::::  |  # PTM #    :::::    :::::       @   |
+  |   #####      ^ ^   |   #####      ^ !      ^ !        .   |   |||||||||
+  | |->###       | !   | |->###       | !      | !        .   |   || DAP ||
+  | |   #        | !   | |   #        | !      | !        .   |   |||||||||
+  | |   .        | !   | |   .        | !      | !        .   |      |  |
+  | |   .        | !   | |   .        | !      | !        .   |      |  *
+  | |   .        | !   | |   .        | !      | !        .   |      | SWD/
+  | |   .        | !   | |   .        | !      | !        .   |      | JTAG
+  *****************************************************************<-|
+ *************************** AMBA Debug APB ************************
+  *****************************************************************
+   |    .          !         .          !        !        .    |
+   |    .          *         .          *        *        .    |
+  *****************************************************************
+ ******************** Cross Trigger Matrix (CTM) *******************
+  *****************************************************************
+   |    .     ^              .                            .    |
+   |    *     !              *                            *    |
+  *****************************************************************
+ ****************** AMBA Advanced Trace Bus (ATB) ******************
+  *****************************************************************
+   |          !                        ===============         |
+   |          *                         ===== F =====<---------|
+   |   :::::::::                         ==== U ====
+   |-->:: CTI ::<!!                       === N ===
+   |   :::::::::  !                        == N ==
+   |    ^         *                        == E ==
+   |    !  &&&&&&&&&       IIIIIII         == L ==
+   |------>&& ETB &&<......II     I        =======
+   |    !  &&&&&&&&&       II     I           .
+   |    !                    I     I          .
+   |    !                    I REP I<..........
+   |    !                    I     I
+   |    !!>&&&&&&&&&       II     I           *Source: ARM ltd.
+   |------>& TPIU  &<......II    I            DAP = Debug Access Port
+           &&&&&&&&&       IIIIIII            ETM = Embedded Trace Macrocell
+               ;                              PTM = Program Trace Macrocell
+               ;                              CTI = Cross Trigger Interface
+               *                              ETB = Embedded Trace Buffer
+          To trace port                       TPIU= Trace Port Interface Unit
+                                              SWD = Serial Wire Debug
+
+While on target configuration of the components is done via the APB bus,
+all trace data are carried out-of-band on the ATB bus.  The CTM provides
+a way to aggregate and distribute signals between CoreSight components.
+
+The coresight framework provides a central point to represent, configure and
+manage coresight devices on a platform.  This first implementation centers on
+the basic tracing functionality, enabling components such ETM/PTM, funnel,
+replicator, TMC, TPIU and ETB.  Future work will enable more
+intricate IP blocks such as STM and CTI.
+
+
+Acronyms and Classification
+---------------------------
+
+Acronyms:
+
+PTM:
+    Program Trace Macrocell
+ETM:
+    Embedded Trace Macrocell
+STM:
+    System trace Macrocell
+ETB:
+    Embedded Trace Buffer
+ITM:
+    Instrumentation Trace Macrocell
+TPIU:
+     Trace Port Interface Unit
+TMC-ETR:
+        Trace Memory Controller, configured as Embedded Trace Router
+TMC-ETF:
+        Trace Memory Controller, configured as Embedded Trace FIFO
+CTI:
+    Cross Trigger Interface
+
+Classification:
+
+Source:
+   ETMv3.x ETMv4, PTMv1.0, PTMv1.1, STM, STM500, ITM
+Link:
+   Funnel, replicator (intelligent or not), TMC-ETR
+Sinks:
+   ETBv1.0, ETB1.1, TPIU, TMC-ETF
+Misc:
+   CTI
+
+
+Device Tree Bindings
+--------------------
+
+See Documentation/devicetree/bindings/arm/coresight.txt for details.
+
+As of this writing drivers for ITM, STMs and CTIs are not provided but are
+expected to be added as the solution matures.
+
+
+Framework and implementation
+----------------------------
+
+The coresight framework provides a central point to represent, configure and
+manage coresight devices on a platform.  Any coresight compliant device can
+register with the framework for as long as they use the right APIs:
+
+.. c:function:: struct coresight_device *coresight_register(struct coresight_desc *desc);
+.. c:function:: void coresight_unregister(struct coresight_device *csdev);
+
+The registering function is taking a ``struct coresight_desc *desc`` and
+register the device with the core framework. The unregister function takes
+a reference to a ``struct coresight_device *csdev`` obtained at registration time.
+
+If everything goes well during the registration process the new devices will
+show up under /sys/bus/coresight/devices, as showns here for a TC2 platform::
+
+    root:~# ls /sys/bus/coresight/devices/
+    replicator  20030000.tpiu    2201c000.ptm  2203c000.etm  2203e000.etm
+    20010000.etb         20040000.funnel  2201d000.ptm  2203d000.etm
+    root:~#
+
+The functions take a ``struct coresight_device``, which looks like this::
+
+    struct coresight_desc {
+            enum coresight_dev_type type;
+            struct coresight_dev_subtype subtype;
+            const struct coresight_ops *ops;
+            struct coresight_platform_data *pdata;
+            struct device *dev;
+            const struct attribute_group **groups;
+    };
+
+
+The "coresight_dev_type" identifies what the device is, i.e, source link or
+sink while the "coresight_dev_subtype" will characterise that type further.
+
+The ``struct coresight_ops`` is mandatory and will tell the framework how to
+perform base operations related to the components, each component having
+a different set of requirement. For that ``struct coresight_ops_sink``,
+``struct coresight_ops_link`` and ``struct coresight_ops_source`` have been
+provided.
+
+The next field ``struct coresight_platform_data *pdata`` is acquired by calling
+``of_get_coresight_platform_data()``, as part of the driver's _probe routine and
+``struct device *dev`` gets the device reference embedded in the ``amba_device``::
+
+    static int etm_probe(struct amba_device *adev, const struct amba_id *id)
+    {
+     ...
+     ...
+     drvdata->dev = &adev->dev;
+     ...
+    }
+
+Specific class of device (source, link, or sink) have generic operations
+that can be performed on them (see ``struct coresight_ops``). The ``**groups``
+is a list of sysfs entries pertaining to operations
+specific to that component only.  "Implementation defined" customisations are
+expected to be accessed and controlled using those entries.
+
+Device Naming scheme
+--------------------
+
+The devices that appear on the "coresight" bus were named the same as their
+parent devices, i.e, the real devices that appears on AMBA bus or the platform bus.
+Thus the names were based on the Linux Open Firmware layer naming convention,
+which follows the base physical address of the device followed by the device
+type. e.g::
+
+    root:~# 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
+
+However, with the introduction of ACPI support, the names of the real
+devices are a bit cryptic and non-obvious. Thus, a new naming scheme was
+introduced to use more generic names based on the type of the device. The
+following rules apply::
+
+  1) Devices that are bound to CPUs, are named based on the CPU logical
+     number.
+
+     e.g, ETM bound to CPU0 is named "etm0"
+
+  2) All other devices follow a pattern, "<device_type_prefix>N", where :
+
+	<device_type_prefix> 	- A prefix specific to the type of the device
+	N			- a sequential number assigned based on the order
+				  of probing.
+
+	e.g, tmc_etf0, tmc_etr0, funnel0, funnel1
+
+Thus, with the new scheme the devices could appear as ::
+
+    root:~# ls /sys/bus/coresight/devices/
+     etm0     etm1     etm2         etm3  etm4      etm5      funnel0
+     funnel1  funnel2  replicator0  stm0  tmc_etf0  tmc_etr0  tpiu0
+
+Some of the examples below might refer to old naming scheme and some
+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
+-----------------------------
+
+There are two ways to use the Coresight framework:
+
+1. using the perf cmd line tools.
+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 identified.
+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
+class will have an "active" entry in sysfs::
+
+    root:/sys/bus/coresight/devices# ls
+    replicator  20030000.tpiu    2201c000.ptm  2203c000.etm  2203e000.etm
+    20010000.etb         20040000.funnel  2201d000.ptm  2203d000.etm
+    root:/sys/bus/coresight/devices# ls 20010000.etb
+    enable_sink  status  trigger_cntr
+    root:/sys/bus/coresight/devices# echo 1 > 20010000.etb/enable_sink
+    root:/sys/bus/coresight/devices# cat 20010000.etb/enable_sink
+    1
+    root:/sys/bus/coresight/devices#
+
+At boot time the current etm3x driver will configure the first address
+comparator with "_stext" and "_etext", essentially tracing any instruction
+that falls within that range.  As such "enabling" a source will immediately
+trigger a trace capture::
+
+    root:/sys/bus/coresight/devices# echo 1 > 2201c000.ptm/enable_source
+    root:/sys/bus/coresight/devices# cat 2201c000.ptm/enable_source
+    1
+    root:/sys/bus/coresight/devices# cat 20010000.etb/status
+    Depth:          0x2000
+    Status:         0x1
+    RAM read ptr:   0x0
+    RAM wrt ptr:    0x19d3   <----- The write pointer is moving
+    Trigger cnt:    0x0
+    Control:        0x1
+    Flush status:   0x0
+    Flush ctrl:     0x2001
+    root:/sys/bus/coresight/devices#
+
+Trace collection is stopped the same way::
+
+    root:/sys/bus/coresight/devices# echo 0 > 2201c000.ptm/enable_source
+    root:/sys/bus/coresight/devices#
+
+The content of the ETB buffer can be harvested directly from /dev::
+
+    root:/sys/bus/coresight/devices# dd if=/dev/20010000.etb \
+    of=~/cstrace.bin
+    64+0 records in
+    64+0 records out
+    32768 bytes (33 kB) copied, 0.00125258 s, 26.2 MB/s
+    root:/sys/bus/coresight/devices#
+
+The file cstrace.bin can be decompressed using "ptm2human", DS-5 or Trace32.
+
+Following is a DS-5 output of an experimental loop that increments a variable up
+to a certain value.  The example is simple and yet provides a glimpse of the
+wealth of possibilities that coresight provides.
+::
+
+    Info                                    Tracing enabled
+    Instruction     106378866       0x8026B53C      E52DE004        false   PUSH     {lr}
+    Instruction     0       0x8026B540      E24DD00C        false   SUB      sp,sp,#0xc
+    Instruction     0       0x8026B544      E3A03000        false   MOV      r3,#0
+    Instruction     0       0x8026B548      E58D3004        false   STR      r3,[sp,#4]
+    Instruction     0       0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+    Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+    Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+    Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+    Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+    Timestamp                                       Timestamp: 17106715833
+    Instruction     319     0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+    Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+    Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+    Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+    Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+    Instruction     9       0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+    Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+    Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+    Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+    Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+    Instruction     7       0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+    Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+    Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+    Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+    Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+    Instruction     7       0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+    Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+    Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+    Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+    Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+    Instruction     10      0x8026B54C      E59D3004        false   LDR      r3,[sp,#4]
+    Instruction     0       0x8026B550      E3530004        false   CMP      r3,#4
+    Instruction     0       0x8026B554      E2833001        false   ADD      r3,r3,#1
+    Instruction     0       0x8026B558      E58D3004        false   STR      r3,[sp,#4]
+    Instruction     0       0x8026B55C      DAFFFFFA        true    BLE      {pc}-0x10 ; 0x8026b54c
+    Instruction     6       0x8026B560      EE1D3F30        false   MRC      p15,#0x0,r3,c13,c0,#1
+    Instruction     0       0x8026B564      E1A0100D        false   MOV      r1,sp
+    Instruction     0       0x8026B568      E3C12D7F        false   BIC      r2,r1,#0x1fc0
+    Instruction     0       0x8026B56C      E3C2203F        false   BIC      r2,r2,#0x3f
+    Instruction     0       0x8026B570      E59D1004        false   LDR      r1,[sp,#4]
+    Instruction     0       0x8026B574      E59F0010        false   LDR      r0,[pc,#16] ; [0x8026B58C] = 0x80550368
+    Instruction     0       0x8026B578      E592200C        false   LDR      r2,[r2,#0xc]
+    Instruction     0       0x8026B57C      E59221D0        false   LDR      r2,[r2,#0x1d0]
+    Instruction     0       0x8026B580      EB07A4CF        true    BL       {pc}+0x1e9344 ; 0x804548c4
+    Info                                    Tracing enabled
+    Instruction     13570831        0x8026B584      E28DD00C        false   ADD      sp,sp,#0xc
+    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 cores), the "cs_etm" PMU will be listed only once.
+
+A Coresight PMU works the same way as any other PMU, 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.
+On newer kernels the available sinks are listed in sysFS under
+($SYSFS)/bus/event_source/devices/cs_etm/sinks/::
+
+	root@localhost:/sys/bus/event_source/devices/cs_etm/sinks# ls
+	tmc_etf0  tmc_etr0  tpiu0
+
+On older kernels, this may need to be found from the list of coresight devices,
+available under ($SYSFS)/bus/coresight/devices/::
+
+	root:~# ls /sys/bus/coresight/devices/
+	 etm0     etm1     etm2         etm3  etm4      etm5      funnel0
+	 funnel1  funnel2  replicator0  stm0  tmc_etf0  tmc_etr0  tpiu0
+	root@linaro-nano:~# perf record -e cs_etm/@tmc_etr0/u --per-thread program
+
+As mentioned above in section "Device Naming scheme", the names of the devices could
+look different from what is used in the example above. One must use the device names
+as it appears under the sysFS.
+
+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 sink
+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 [#third]_.
+
+2.1) AutoFDO analysis using the perf tools:
+
+perf can be used to record and analyze trace of programs.
+
+Execution can be recorded using 'perf record' with the cs_etm event,
+specifying the name of the sink to record to, e.g::
+
+    perf record -e cs_etm/@tmc_etr0/u --per-thread
+
+The 'perf report' and 'perf script' commands can be used to analyze execution,
+synthesizing instruction and branch events from the instruction trace.
+'perf inject' can be used to replace the trace data with the synthesized events.
+The --itrace option controls the type and frequency of synthesized events
+(see perf documentation).
+
+Note that only 64-bit programs are currently supported - further work is
+required to support instruction decode of 32-bit Arm programs.
+
+
+Generating coverage files for Feedback Directed Optimization: AutoFDO
+---------------------------------------------------------------------
+
+'perf inject' accepts the --itrace option in which case tracing data is
+removed and replaced with the synthesized events. e.g.
+::
+
+	perf inject --itrace --strip -i perf.data -o perf.data.new
+
+Below is an example of using ARM ETM for autoFDO.  It requires autofdo
+(https://github.com/google/autofdo) and gcc version 5.  The bubble
+sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tutorial).
+::
+
+	$ gcc-5 -O3 sort.c -o sort
+	$ taskset -c 2 ./sort
+	Bubble sorting array of 30000 elements
+	5910 ms
+
+	$ perf record -e cs_etm/@tmc_etr0/u --per-thread taskset -c 2 ./sort
+	Bubble sorting array of 30000 elements
+	12543 ms
+	[ perf record: Woken up 35 times to write data ]
+	[ perf record: Captured and wrote 69.640 MB perf.data ]
+
+	$ perf inject -i perf.data -o inj.data --itrace=il64 --strip
+	$ create_gcov --binary=./sort --profile=inj.data --gcov=sort.gcov -gcov_version=1
+	$ gcc-5 -O3 -fauto-profile=sort.gcov sort.c -o sort_autofdo
+	$ taskset -c 2 ./sort_autofdo
+	Bubble sorting array of 30000 elements
+	5806 ms
+
+
+How to use the STM module
+-------------------------
+
+Using the System Trace Macrocell module is the same as the tracers - the only
+difference is that clients are driving the trace capture rather
+than the program flow through the code.
+
+As with any other CoreSight component, specifics about the STM tracer can be
+found in sysfs with more information on each entry being found in [#first]_::
+
+    root@genericarmv8:~# ls /sys/bus/coresight/devices/stm0
+    enable_source   hwevent_select  port_enable     subsystem       uevent
+    hwevent_enable  mgmt            port_select     traceid
+    root@genericarmv8:~#
+
+Like any other source a sink needs to be identified and the STM enabled before
+being used::
+
+    root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/tmc_etf0/enable_sink
+    root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/stm0/enable_source
+
+From there user space applications can request and use channels using the devfs
+interface provided for that purpose by the generic STM API::
+
+    root@genericarmv8:~# ls -l /dev/stm0
+    crw-------    1 root     root       10,  61 Jan  3 18:11 /dev/stm0
+    root@genericarmv8:~#
+
+Details on how to use the generic STM API can be found here:- :doc:`../stm` [#second]_.
+
+The CTI & CTM Modules
+---------------------
+
+The CTI (Cross Trigger Interface) provides a set of trigger signals between
+individual CTIs and components, and can propagate these between all CTIs via
+channels on the CTM (Cross Trigger Matrix).
+
+A separate documentation file is provided to explain the use of these devices.
+(:doc:`coresight-ect`) [#fourth]_.
+
+
+.. [#first] Documentation/ABI/testing/sysfs-bus-coresight-devices-stm
+
+.. [#second] Documentation/trace/stm.rst
+
+.. [#third] https://github.com/Linaro/perf-opencsd
+
+.. [#fourth] Documentation/trace/coresight/coresight-ect.rst