diff mbox series

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

Message ID 20191119231912.12768-14-mike.leach@linaro.org
State Superseded
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

-- 
2.17.1

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>




-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK
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