Commit f9809d56 authored by Mike Leach's avatar Mike Leach Committed by Mathieu Poirier
Browse files

Documentation: coresight: Update coresight configuration docs 



Update the CoreSight System Configuration document to cover the
use of loadable modules to add configurations and features
to the system.

Signed-off-by: default avatarMike Leach <mike.leach@linaro.org>
Link: https://lore.kernel.org/r/20211124200038.28662-7-mike.leach@linaro.org


Signed-off-by: default avatarMathieu Poirier <mathieu.poirier@linaro.org>
parent 7ebd0ec6

Documentation/trace/coresight/coresight-config.rst

+59 −3
Original line number Diff line number Diff line
@@ -155,14 +155,14 @@ follows:: 
    autofdo

    $ cd autofdo/

    $ ls

    description   preset1  preset3  preset5  preset7  preset9

    feature_refs  preset2  preset4  preset6  preset8

    description  feature_refs  preset1  preset3  preset5  preset7  preset9

    enable       preset        preset2  preset4  preset6  preset8

    $ cat description

    Setup ETMs with strobing for autofdo

    $ cat feature_refs

    strobing



Each preset declared has a preset<n> subdirectory declared. The values for

Each preset declared has a 'preset<n>' subdirectory declared. The values for

the preset can be examined::



    $ cat preset1/values
@@ -170,6 +170,9 @@ the preset can be examined:: 
    $ cat preset2/values

    strobing.window = 0x1388 strobing.period = 0x4



The 'enable' and 'preset' files allow the control of a configuration when

using CoreSight with sysfs.



The features referenced by the configuration can be examined in the features

directory::
@@ -236,3 +239,56 @@ A preset to override the current parameter values can also be selected:: 


When configurations are selected in this way, then the trace sink used is

automatically selected.



Using Configurations in sysfs

=============================



Coresight can be controlled using sysfs. When this is in use then a configuration

can be made active for the devices that are used in the sysfs session.



In a configuration there are 'enable' and 'preset' files.



To enable a configuration for use with sysfs::



    $ cd configurations/autofdo

    $ echo 1 > enable



This will then use any default parameter values in the features - which can be

adjusted as described above.



To use a preset<n> set of parameter values::



    $ echo 3 > preset



This will select preset3 for the configuration.

The valid values for preset are 0 - to deselect presets, and any value of

<n> where a preset<n> sub-directory is present.



Note that the active sysfs configuration is a global parameter, therefore

only a single configuration can be active for sysfs at any one time.

Attempting to enable a second configuration will result in an error.

Additionally, attempting to disable the configuration while in use will

also result in an error.



The use of the active configuration by sysfs is independent of the configuration

used in perf.





Creating and Loading Custom Configurations

==========================================



Custom configurations and / or features can be dynamically loaded into the

system by using a loadable module.



An example of a custom configuration is found in ./samples/coresight.



This creates a new configuration that uses the existing built in

strobing feature, but provides a different set of presets.



When the module is loaded, then the configuration appears in the configfs

file system and is selectable in the same way as the built in configuration

described above.



Configurations can use previously loaded features. The system will ensure

that it is not possible to unload a feature that is currently in use, by

enforcing the unload order as the strict reverse of the load order.