Merge tag 'docs-4.18' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "There's been a fair amount of work in the docs tree this time around,
  including:

   - Extensive RST conversions and organizational work in the
     memory-management docs thanks to Mike Rapoport.

   - An update of Documentation/features from Andrea Parri and a script
     to keep it updated.

   - Various LICENSES updates from Thomas, along with a script to check
     SPDX tags.

   - Work to fix dangling references to documentation files; this
     involved a fair number of one-liner comment changes outside of
     Documentation/

  ... and the usual list of documentation improvements, typo fixes, etc"

* tag 'docs-4.18' of git://git.lwn.net/linux: (103 commits)
  Documentation: document hung_task_panic kernel parameter
  docs/admin-guide/mm: add high level concepts overview
  docs/vm: move ksm and transhuge from "user" to "internals" section.
  docs: Use the kerneldoc comments for memalloc_no*()
  doc: document scope NOFS, NOIO APIs
  docs: update kernel versions and dates in tables
  docs/vm: transhuge: split userspace bits to admin-guide/mm/transhuge
  docs/vm: transhuge: minor updates
  docs/vm: transhuge: change sections order
  Documentation: arm: clean up Marvell Berlin family info
  Documentation: gpio: driver: Fix a typo and some odd grammar
  docs: ranoops.rst: fix location of ramoops.txt
  scripts/documentation-file-ref-check: rewrite it in perl with auto-fix mode
  docs: uio-howto.rst: use a code block to solve a warning
  mm, THP, doc: Add document for thp_swpout/thp_swpout_fallback
  w1: w1_io.c: fix a kernel-doc warning
  Documentation/process/posting: wrap text at 80 cols
  docs: admin-guide: add cgroup-v2 documentation
  Revert "Documentation/features/vm: Remove arch support status file for 'pte_special'"
  Documentation: refcount-vs-atomic: Update reference to LKMM doc.
  ...

1 files changed, 75 insertions, 28 deletions

diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt
index 6f0120c3a4f1..1d74ad0202b6 100644
--- a/Documentation/trace/coresight.txt
+++ b/Documentation/trace/coresight.txt
@@ -187,13 +187,19 @@ 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.
 
-Last but not least, "struct module *owner" is expected to be set to reflect
-the information carried in "THIS_MODULE".
 
 How to use the tracer modules
 -----------------------------
 
-Before trace collection can start, a coresight sink needs to be identify.
+There are 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 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:
@@ -298,42 +304,48 @@ Instruction     13570831        0x8026B584      E28DD00C        false   ADD
 Instruction     0       0x8026B588      E8BD8000        true    LDM      sp!,{pc}
 Timestamp                                       Timestamp: 17107041535
 
-How to use the STM module
--------------------------
+2) Using perf framework:
 
-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.
+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:
 
-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 [1]:
+	linaro@linaro-nano:~$ ./perf list pmu
 
-root@genericarmv8:~# ls /sys/bus/coresight/devices/20100000.stm
-enable_source   hwevent_select  port_enable     subsystem       uevent
-hwevent_enable  mgmt            port_select     traceid
-root@genericarmv8:~#
+		List of pre-defined events (to be used in -e):
 
-Like any other source a sink needs to be identified and the STM enabled before
-being used:
+		cs_etm//                                    [Kernel PMU event]
 
-root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20010000.etf/enable_sink
-root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20100000.stm/enable_source
+	linaro@linaro-nano:~$
 
-From there user space applications can request and use channels using the devfs
-interface provided for that purpose by the generic STM API:
+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.
 
-root@genericarmv8:~# ls -l /dev/20100000.stm
-crw-------    1 root     root       10,  61 Jan  3 18:11 /dev/20100000.stm
-root@genericarmv8:~#
+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.  Names for sink to choose
+from are listed in sysFS under ($SYSFS)/bus/coresight/devices:
 
-Details on how to use the generic STM API can be found here [2].
+	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
 
-[1]. Documentation/ABI/testing/sysfs-bus-coresight-devices-stm
-[2]. Documentation/trace/stm.txt
+	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 sink
+to use for the trace session.
 
-Using perf tools
-----------------
+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].
+
+2.1) AutoFDO analysis using the perf tools:
 
 perf can be used to record and analyze trace of programs.
 
@@ -381,3 +393,38 @@ sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tuto
 	$ 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 [1]:
+
+root@genericarmv8:~# ls /sys/bus/coresight/devices/20100000.stm
+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/20010000.etf/enable_sink
+root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20100000.stm/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/20100000.stm
+crw-------    1 root     root       10,  61 Jan  3 18:11 /dev/20100000.stm
+root@genericarmv8:~#
+
+Details on how to use the generic STM API can be found here [2].
+
+[1]. Documentation/ABI/testing/sysfs-bus-coresight-devices-stm
+[2]. Documentation/trace/stm.txt
+[3]. https://github.com/Linaro/perf-opencsd