docs: coresight: Update documentation for CoreSight to cover CTI

Add new document covering CTI / CTM usage in CoreSight.

Add section in coresight.rst introducing CTI and CTM modules with link
to new document.

Signed-off-by: Mike Leach <mike.leach@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200320165303.13681-11-mathieu.poirier@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 235 insertions, 0 deletions

diff --git a/Documentation/trace/coresight/coresight-ect.rst b/Documentation/trace/coresight/coresight-ect.rst
new file mode 100644
index 000000000000..ecc1e57012ef
--- /dev/null
+++ b/Documentation/trace/coresight/coresight-ect.rst
@@ -0,0 +1,222 @@
+.. SPDX-License-Identifier: GPL-2.0
+=============================================
+CoreSight Embedded Cross Trigger (CTI & CTM).
+=============================================
+
+    :Author:   Mike Leach <mike.leach@linaro.org>
+    :Date:     November 2019
+
+Hardware Description
+--------------------
+
+The CoreSight Cross Trigger Interface (CTI) is a hardware device that takes
+individual input and output hardware signals known as triggers to and from
+devices and interconnects them via the Cross Trigger Matrix (CTM) to other
+devices via numbered channels, in order to propagate events between devices.
+
+e.g.::
+
+ 0000000  in_trigs  :::::::
+ 0 C   0----------->:     :             +======>(other CTI channel IO)
+ 0  P  0<-----------:     :             v
+ 0   U 0  out_trigs :     : Channels  *****      :::::::
+ 0000000            : CTI :<=========>*CTM*<====>: CTI :---+
+ #######  in_trigs  :     : (id 0-3)  *****      :::::::   v
+ # ETM #----------->:     :                         ^   #######
+ #     #<-----------:     :                         +---# ETR #
+ ####### out_trigs  :::::::                             #######
+
+The CTI driver enables the programming of the CTI to attach triggers to
+channels. When an input trigger becomes active, the attached channel will
+become active. Any output trigger attached to that channel will also
+become active. The active channel is propagated to other CTIs via the CTM,
+activating connected output triggers there, unless filtered by the CTI
+channel gate.
+
+It is also possible to activate a channel using system software directly
+programming registers in the CTI.
+
+The CTIs are registered by the system to be associated with CPUs and/or other
+CoreSight devices on the trace data path. When these devices are enabled the
+attached CTIs will also be enabled. By default/on power up the CTIs have
+no programmed trigger/channel attachments, so will not affect the system
+until explicitly programmed.
+
+The hardware trigger connections between CTIs and devices is implementation
+defined, unless the CPU/ETM combination is a v8 architecture, in which case
+the connections have an architecturally defined standard layout.
+
+The hardware trigger signals can also be connected to non-CoreSight devices
+(e.g. UART), or be propagated off chip as hardware IO lines.
+
+All the CTI devices are associated with a CTM. On many systems there will be a
+single effective CTM (one CTM, or multiple CTMs all interconnected), but it is
+possible that systems can have nets of CTIs+CTM that are not interconnected by
+a CTM to each other. On these systems a CTM index is declared to associate
+CTI devices that are interconnected via a given CTM.
+
+Sysfs files and directories
+---------------------------
+
+The CTI devices appear on the existing CoreSight bus alongside the other
+CoreSight devices::
+
+    >$ ls /sys/bus/coresight/devices
+     cti_cpu0  cti_cpu2  cti_sys0  etm0  etm2  funnel0  replicator0  tmc_etr0
+     cti_cpu1  cti_cpu3  cti_sys1  etm1  etm3  funnel1  tmc_etf0     tpiu0
+
+The ``cti_cpu<N>`` named CTIs are associated with a CPU, and any ETM used by
+that core. The ``cti_sys<N>`` CTIs are general system infrastructure CTIs that
+can be associated with other CoreSight devices, or other system hardware
+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
+
+*Key file items are:-*
+   * ``enable``: enables/disables the CTI. Read to determine current state.
+     If this shows as enabled (1), but ``powered`` shows unpowered (0), then
+     the enable indicates a request to enabled when the device is powered.
+   * ``ctmid`` : associated CTM - only relevant if system has multiple CTI+CTM
+     clusters that are not interconnected.
+   * ``nr_trigger_cons`` : total connections - triggers<N> directories.
+   * ``powered`` : Read to determine if the CTI is currently powered.
+
+*Sub-directories:-*
+   * ``triggers<N>``: contains list of triggers for an individual connection.
+   * ``channels``: Contains the channel API - CTI main programming interface.
+   * ``regs``: Gives access to the raw programmable CTI regs.
+   * ``mgmt``: the standard CoreSight management registers.
+
+
+triggers<N> directories
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Individual trigger connection information. This describes trigger signals for
+CoreSight and non-CoreSight connections.
+
+Each triggers directory has a set of parameters describing the triggers for
+the connection.
+
+   * ``name`` : name of connection
+   * ``in_signals`` : input trigger signal indexes used in this connection.
+   * ``in_types`` : functional types for in signals.
+   * ``out_signals`` : output trigger signals for this connection.
+   * ``out_types`` : functional types for out signals.
+
+e.g::
+
+    >$ ls ./cti_cpu0/triggers0/
+    in_signals  in_types  name  out_signals  out_types
+    >$ cat ./cti_cpu0/triggers0/name
+    cpu0
+    >$ cat ./cti_cpu0/triggers0/out_signals
+    0-2
+    >$ cat ./cti_cpu0/triggers0/out_types
+    pe_edbgreq pe_dbgrestart pe_ctiirq
+    >$ cat ./cti_cpu0/triggers0/in_signals
+    0-1
+    >$ cat ./cti_cpu0/triggers0/in_types
+    pe_dbgtrigger pe_pmuirq
+
+If a connection has zero signals in either the 'in' or 'out' triggers then
+those parameters will be omitted.
+
+Channels API Directory
+~~~~~~~~~~~~~~~~~~~~~~
+
+This provides an easy way to attach triggers to channels, without needing
+the multiple register operations that are required if manipulating the
+'regs' sub-directory elements directly.
+
+A number of files provide this API::
+
+   >$ ls ./cti_sys0/channels/
+   chan_clear         chan_inuse      chan_xtrigs_out     trigin_attach
+   chan_free          chan_pulse      chan_xtrigs_reset   trigin_detach
+   chan_gate_disable  chan_set        chan_xtrigs_sel     trigout_attach
+   chan_gate_enable   chan_xtrigs_in  trig_filter_enable  trigout_detach
+   trigout_filtered
+
+Most access to these elements take the form::
+
+  echo <chan> [<trigger>] > /<device_path>/<operation>
+
+where the optional <trigger> is only needed for trigXX_attach | detach
+operations.
+
+e.g.::
+
+   >$ echo 0 1 > ./cti_sys0/channels/trigout_attach
+   >$ echo 0 > ./cti_sys0/channels/chan_set
+
+Attaches trigout(1) to channel(0), then activates channel(0) generating a
+set state on cti_sys0.trigout(1)
+
+
+*API operations*
+
+   * ``trigin_attach, trigout_attach``: Attach a channel to a trigger signal.
+   * ``trigin_detach, trigout_detach``: Detach a channel from a trigger signal.
+   * ``chan_set``: Set the channel - the set state will be propagated around
+     the CTM to other connected devices.
+   * ``chan_clear``: Clear the channel.
+   * ``chan_pulse``: Set the channel for a single CoreSight clock cycle.
+   * ``chan_gate_enable``: Write operation sets the CTI gate to propagate
+     (enable) the channel to other devices. This operation takes a channel
+     number. CTI gate is enabled for all channels by default at power up. Read
+     to list the currently enabled channels on the gate.
+   * ``chan_gate_disable``: Write channel number to disable gate for that
+     channel.
+   * ``chan_inuse``: Show the current channels attached to any signal
+   * ``chan_free``: Show channels with no attached signals.
+   * ``chan_xtrigs_sel``: write a channel number to select a channel to view,
+     read to show the selected channel number.
+   * ``chan_xtrigs_in``: Read to show the input triggers attached to
+     the selected view channel.
+   * ``chan_xtrigs_out``:Read to show the output triggers attached to
+     the selected view channel.
+   * ``trig_filter_enable``: Defaults to enabled, disable to allow potentially
+     dangerous output signals to be set.
+   * ``trigout_filtered``: Trigger out signals that are prevented from being
+     set if filtering ``trig_filter_enable`` is enabled. One use is to prevent
+     accidental ``EDBGREQ`` signals stopping a core.
+   * ``chan_xtrigs_reset``: Write 1 to clear all channel / trigger programming.
+     Resets device hardware to default state.
+
+
+The example below attaches input trigger index 1 to channel 2, and output
+trigger index 6 to the same channel. It then examines the state of the
+channel / trigger connections using the appropriate sysfs attributes.
+
+The settings mean that if either input trigger 1, or channel 2 go active then
+trigger out 6 will go active. We then enable the CTI, and use the software
+channel control to activate channel 2. We see the active channel on the
+``choutstatus`` register and the active signal on the ``trigoutstatus``
+register. Finally clearing the channel removes this.
+
+e.g.::
+
+   .../cti_sys0/channels# echo 2 1 > trigin_attach
+   .../cti_sys0/channels# echo 2 6 > trigout_attach
+   .../cti_sys0/channels# cat chan_free
+   0-1,3
+   .../cti_sys0/channels# cat chan_inuse
+   2
+   .../cti_sys0/channels# echo 2 > chan_xtrigs_sel
+   .../cti_sys0/channels# cat chan_xtrigs_trigin
+   1
+   .../cti_sys0/channels# cat chan_xtrigs_trigout
+   6
+   .../cti_sys0/# echo 1 > enable
+   .../cti_sys0/channels# echo 2 > chan_set
+   .../cti_sys0/channels# cat ../regs/choutstatus
+   0x4
+   .../cti_sys0/channels# cat ../regs/trigoutstatus
+   0x40
+   .../cti_sys0/channels# echo 2 > chan_clear
+   .../cti_sys0/channels# cat ../regs/trigoutstatus
+   0x0
+   .../cti_sys0/channels# cat ../regs/choutstatus
+   0x0
diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst
index a566719f8e7e..108600ee1e12 100644
--- a/Documentation/trace/coresight/coresight.rst
+++ b/Documentation/trace/coresight/coresight.rst
@@ -491,8 +491,21 @@ interface provided for that purpose by the generic STM API::
 
 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