diff mbox series

[v5,13/14] docs: coresight: Update documentation for CoreSight to cover CTI.

Message ID 20191119231912.12768-14-mike.leach@linaro.org (mailing list archive)
State New, archived
Headers show
Series CoreSight CTI Driver | expand

Commit Message

Mike Leach Nov. 19, 2019, 11:19 p.m. UTC 
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>
---
 .../trace/coresight/coresight-ect.rst         | 200 ++++++++++++++++++
 Documentation/trace/coresight/coresight.rst   |  13 ++
 2 files changed, 213 insertions(+)
 create mode 100644 Documentation/trace/coresight/coresight-ect.rst

Comments

Mathieu Poirier Nov. 27, 2019, 7 p.m. UTC | #1 
On Tue, Nov 19, 2019 at 11:19:11PM +0000, Mike Leach wrote:
> 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>
> ---
>  .../trace/coresight/coresight-ect.rst         | 200 ++++++++++++++++++
>  Documentation/trace/coresight/coresight.rst   |  13 ++
>  2 files changed, 213 insertions(+)
>  create mode 100644 Documentation/trace/coresight/coresight-ect.rst
> 
> diff --git a/Documentation/trace/coresight/coresight-ect.rst b/Documentation/trace/coresight/coresight-ect.rst
> new file mode 100644
> index 000000000000..6448cf910f20
> --- /dev/null
> +++ b/Documentation/trace/coresight/coresight-ect.rst
> @@ -0,0 +1,200 @@
> +=============================================
> +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,
> +activiating connected output triggers there, unless filtered by the CTI

s/activiating/activating

> +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  regs  subsystem
> +  triggers0 triggers1  uevent
> +
> +*Key file items are:-*
> +   * ``enable``: enables/disables the CTI.
> +   * ``ctmid`` : associated CTM - only relevant if system has multiple CTI+CTM
> +     clusters that are not interconnected.
> +   * ``nr_trigger_cons`` : total connections - triggers<N> directories.
> +
> +*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 manipluating the

s/manipluating/manipulating

> +'regs' sub-dir elements directly.
> +
> +A number of files provide this API::
> +
> +   >$ ls ./cti_sys0/channels/
> +   chan_clear         chan_inuse         chan_xtrigs_view      trigin_detach
> +   chan_free          chan_pulse         chan_xtrigs_view_sel  trigout_attach
> +   chan_gate_disable  chan_set           trig_filter_enable    trigout_detach
> +   chan_gate_enable   chan_xtrigs_reset  trigin_attach         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 propogated around

s/propogated/propagated

This patch will be handled by Jonathan Corbet and as such he needs to be CC'ed
in your next submission. 

> +     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_xtrig_view``: write a channel number to select a channel to view,
> +     read to show the cross triggers programmed for the selected 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.
> +
> +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_view
> +   .../cti_sys0/channels# cat chan_xtrigs_view
> +   [2] IN: 1 OUT: 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/trigoutstatus
> +   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
> -- 
> 2.17.1
>
Suzuki K Poulose Dec. 2, 2019, 10:43 a.m. UTC | #2 
On 19/11/2019 23:19, Mike Leach wrote:
> 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>
> ---
>   .../trace/coresight/coresight-ect.rst         | 200 ++++++++++++++++++
>   Documentation/trace/coresight/coresight.rst   |  13 ++
>   2 files changed, 213 insertions(+)
>   create mode 100644 Documentation/trace/coresight/coresight-ect.rst
> 
> diff --git a/Documentation/trace/coresight/coresight-ect.rst b/Documentation/trace/coresight/coresight-ect.rst
> new file mode 100644
> index 000000000000..6448cf910f20
> --- /dev/null
> +++ b/Documentation/trace/coresight/coresight-ect.rst
> @@ -0,0 +1,200 @@
> +=============================================
> +CoreSight Embedded Cross Trigger (CTI & CTM).
> +=============================================
> +
> +    :Author:   Mike Leach <mike.leach@linaro.org>
> +    :Date:     November 2019
> +

...


> +
> +Channels API Directory
> +~~~~~~~~~~~~~~~~~~~~~~
> +
> +This provides an easy way to attach triggers to channels, without needing
> +the multiple register operations that are required if manipluating the
> +'regs' sub-dir elements directly.
> +
> +A number of files provide this API::
> +
> +   >$ ls ./cti_sys0/channels/
> +   chan_clear         chan_inuse         chan_xtrigs_view      trigin_detach
> +   chan_free          chan_pulse         chan_xtrigs_view_sel  trigout_attach
> +   chan_gate_disable  chan_set           trig_filter_enable    trigout_detach
> +   chan_gate_enable   chan_xtrigs_reset  trigin_attach         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 propogated 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_xtrig_view``: write a channel number to select a channel to view,
> +     read to show the cross triggers programmed for the selected 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.
> +
> +e.g.::
> +
> +   .../cti_sys0/channels# echo 2 1 > trigin_attach
> +   .../cti_sys0/channels# echo 2 6 > trigout_attach

minor nit: It may be a good idea to add a comment to describe what you
are doing with the above operations, to avoid looking up and mapping it
for someone looking it up. I am not too keen, but it is definitely
helpful.

> +   .../cti_sys0/channels# cat chan_free
> +   0-1,3
> +   .../cti_sys0/channels# cat chan_inuse
> +   2
> +   .../cti_sys0/channels# echo 2 > chan_xtrigs_view
> +   .../cti_sys0/channels# cat chan_xtrigs_view
> +   [2] IN: 1 OUT: 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/trigoutstatus
> +   0x0

nit: duplicate lines ?

Otherwise:

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Mike Leach Dec. 6, 2019, 5:39 p.m. UTC | #3 
Mathieu, Suzuki,

Fixed per you suggestions.

Thanks

Mike

On Mon, 2 Dec 2019 at 10:43, Suzuki Kuruppassery Poulose
<suzuki.poulose@arm.com> wrote:
>
> On 19/11/2019 23:19, Mike Leach wrote:
> > 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>
> > ---
> >   .../trace/coresight/coresight-ect.rst         | 200 ++++++++++++++++++
> >   Documentation/trace/coresight/coresight.rst   |  13 ++
> >   2 files changed, 213 insertions(+)
> >   create mode 100644 Documentation/trace/coresight/coresight-ect.rst
> >
> > diff --git a/Documentation/trace/coresight/coresight-ect.rst b/Documentation/trace/coresight/coresight-ect.rst
> > new file mode 100644
> > index 000000000000..6448cf910f20
> > --- /dev/null
> > +++ b/Documentation/trace/coresight/coresight-ect.rst
> > @@ -0,0 +1,200 @@
> > +=============================================
> > +CoreSight Embedded Cross Trigger (CTI & CTM).
> > +=============================================
> > +
> > +    :Author:   Mike Leach <mike.leach@linaro.org>
> > +    :Date:     November 2019
> > +
>
> ...
>
>
> > +
> > +Channels API Directory
> > +~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +This provides an easy way to attach triggers to channels, without needing
> > +the multiple register operations that are required if manipluating the
> > +'regs' sub-dir elements directly.
> > +
> > +A number of files provide this API::
> > +
> > +   >$ ls ./cti_sys0/channels/
> > +   chan_clear         chan_inuse         chan_xtrigs_view      trigin_detach
> > +   chan_free          chan_pulse         chan_xtrigs_view_sel  trigout_attach
> > +   chan_gate_disable  chan_set           trig_filter_enable    trigout_detach
> > +   chan_gate_enable   chan_xtrigs_reset  trigin_attach         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 propogated 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_xtrig_view``: write a channel number to select a channel to view,
> > +     read to show the cross triggers programmed for the selected 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.
> > +
> > +e.g.::
> > +
> > +   .../cti_sys0/channels# echo 2 1 > trigin_attach
> > +   .../cti_sys0/channels# echo 2 6 > trigout_attach
>
> minor nit: It may be a good idea to add a comment to describe what you
> are doing with the above operations, to avoid looking up and mapping it
> for someone looking it up. I am not too keen, but it is definitely
> helpful.
>
> > +   .../cti_sys0/channels# cat chan_free
> > +   0-1,3
> > +   .../cti_sys0/channels# cat chan_inuse
> > +   2
> > +   .../cti_sys0/channels# echo 2 > chan_xtrigs_view
> > +   .../cti_sys0/channels# cat chan_xtrigs_view
> > +   [2] IN: 1 OUT: 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/trigoutstatus
> > +   0x0
>
> nit: duplicate lines ?
>
> Otherwise:
>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
diff mbox series

Patch

diff --git a/Documentation/trace/coresight/coresight-ect.rst b/Documentation/trace/coresight/coresight-ect.rst
new file mode 100644
index 000000000000..6448cf910f20
--- /dev/null
+++ b/Documentation/trace/coresight/coresight-ect.rst
@@ -0,0 +1,200 @@ 
+=============================================
+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,
+activiating 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  regs  subsystem
+  triggers0 triggers1  uevent
+
+*Key file items are:-*
+   * ``enable``: enables/disables the CTI.
+   * ``ctmid`` : associated CTM - only relevant if system has multiple CTI+CTM
+     clusters that are not interconnected.
+   * ``nr_trigger_cons`` : total connections - triggers<N> directories.
+
+*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 manipluating the
+'regs' sub-dir elements directly.
+
+A number of files provide this API::
+
+   >$ ls ./cti_sys0/channels/
+   chan_clear         chan_inuse         chan_xtrigs_view      trigin_detach
+   chan_free          chan_pulse         chan_xtrigs_view_sel  trigout_attach
+   chan_gate_disable  chan_set           trig_filter_enable    trigout_detach
+   chan_gate_enable   chan_xtrigs_reset  trigin_attach         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 propogated 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_xtrig_view``: write a channel number to select a channel to view,
+     read to show the cross triggers programmed for the selected 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.
+
+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_view
+   .../cti_sys0/channels# cat chan_xtrigs_view
+   [2] IN: 1 OUT: 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/trigoutstatus
+   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