[PATCH v3 6/6] Documentation: coresight: Update coresight configuration docs

[Mike Leach]

HI Mathieu,

On Fri, 26 Nov 2021 at 18:26, Mathieu Poirier
<mathieu.poirier at linaro.org> wrote:
>
> On Wed, Nov 24, 2021 at 08:00:38PM +0000, Mike Leach wrote:
> > Update the CoreSight System Configuration document to cover the
> > use of loadable modules to add configurations and features
> > to the system.
> >
> > Signed-off-by: Mike Leach <mike.leach at linaro.org>
> > ---
> >  .../trace/coresight/coresight-config.rst      | 62 ++++++++++++++++++-
> >  1 file changed, 59 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/trace/coresight/coresight-config.rst b/Documentation/trace/coresight/coresight-config.rst
> > index 6ed13398ca2c..6d5ffa6f7347 100644
> > --- a/Documentation/trace/coresight/coresight-config.rst
> > +++ b/Documentation/trace/coresight/coresight-config.rst
> > @@ -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.
> > +
>
> Shouldn't all instances in the above section be configfs rather than sysfs?  If
> so should I make the changes?
>

What I am trying to explain there is that when using sysfs to control
CoreSight, it is possible to set a configuration using configfs, which
is then used when a tracer is enabled under sysfs.

Mike


> I have your patchset on stanby in my local coresight-next tree - just let me
> know.
>
> Thanks,
> Mathieu
>
> > +
> > +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.
> > --
> > 2.17.1
> >



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