[PATCH v2 6/6] Documentation: coresight: docs for config load via configfs
Mike Leach
mike.leach at linaro.org
Tue Jan 18 08:41:15 PST 2022
Hi Mathieu,
On Thu, 13 Jan 2022 at 18:16, Mathieu Poirier
<mathieu.poirier at linaro.org> wrote:
>
> More comments...
>
> On Tue, Nov 30, 2021 at 10:01:00PM +0000, Mike Leach wrote:
> > Add documentation covering the configfs updates that allow
> > binary configuration files to be loaded and unloaded via configfs,
> > along with the demonstration programs in samples.
> >
> > Signed-off-by: Mike Leach <mike.leach at linaro.org>
> > ---
> > .../trace/coresight/coresight-config.rst | 151 +++++++++++++++++-
> > 1 file changed, 145 insertions(+), 6 deletions(-)
> >
> > diff --git a/Documentation/trace/coresight/coresight-config.rst b/Documentation/trace/coresight/coresight-config.rst
> > index 6d5ffa6f7347..f11def230fab 100644
> > --- a/Documentation/trace/coresight/coresight-config.rst
> > +++ b/Documentation/trace/coresight/coresight-config.rst
> > @@ -152,7 +152,7 @@ follows::
> >
> > $ cd configurations/
> > $ ls
> > - autofdo
> > + autofdo last_load_status load unload
> > $ cd autofdo/
> > $ ls
> > description feature_refs preset1 preset3 preset5 preset7 preset9
> > @@ -278,9 +278,19 @@ Creating and Loading Custom Configurations
> > ==========================================
> >
> > Custom configurations and / or features can be dynamically loaded into the
> > -system by using a loadable module.
> > +system by using a loadable module, or by loading a binary configuration
> > +file in configfs.
> > +
> > +Loaded 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.
> > +
> > +An example of a custom configuration module, and generators for binary
> > +configuration files are found in './samples/coresight'.
> >
> > -An example of a custom configuration is found in ./samples/coresight.
> > +
> > +Using a Loadable Module
> > +-----------------------
> >
> > This creates a new configuration that uses the existing built in
> > strobing feature, but provides a different set of presets.
> > @@ -289,6 +299,135 @@ 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.
> > +The file 'coresight-cfg-sample.c' contains the configuration and module
> > +initialisation code needed to create the loadable module.
> > +
> > +This will be built alongside the kernel modules if select in KConfig.
> > +
> > +
> > +Using a Binary Configuration File
> > +---------------------------------
> > +
> > +Building the samples creates the 'coresight-cfg-filegen' program that will
> > +generate a configuration binary 'example1.cscfg' that can be loaded into the
> > +system using configfs. The configuration declared in the source file
> > +'coresight-cfg-filegen.c' is named 'autofdo3' - the name that will be used
> > +once loaded.
> > +
> > +The source files 'coresight-cfg-bufw.h' and 'coresight-cfg-bufw.c' provide a
> > +standard function to convert a configuration declared in 'C' into the correct
> > +binary buffer format. These files can be re-used to create new custom
> > +configurations.
> > +
> > +The program 'coresight-cfg-file-read' can read back and print a configuration
> > +binary. This is built using the reader from the driver code.
> > +
> > +There are additional attributes in the configurations directory - load, unload
> > +and last_load_status that can be used to load and unload configuration
> > +binary files. To load, 'cat' the binary config into the load attribute::
> > +
> > + $ ls /config/cs-syscfg/configurations/
> > + autofdo last_load_status load unload
> > + $ cat example1.cscfg > /config/cs-syscfg/configurations/load
> > + $ ls /config/cs-syscfg/configurations/
> > + autofdo autofdo3 last_load_status load unload
> > + $ cat /config/cs-syscfg/configurations/last_load_status
> > + OK: configuration file loaded (autofdo3).
> > +
> > +To unload, use the same file in the unload attribute::
> > +
> > + $ cat example1.cscfg > /config/cs-syscfg/configurations/unload
> > + $ cat /config/cs-syscfg/configurations/last_load_status
> > + OK: configuration file unloaded (autofdo3).
> > + ls /config/cs-syscfg/configurations/
> > + autofdo last_load_status load unload
>
> I'm not certain that "last_load_status" is needed. To me seeing the name of a
> newly added configuration should be enough to confirm a successful status. The
> same applies to unload.
>
Again - this makes more sense after the next ETM patchset that uses
resource management - this status is more useful when features or
configurations fail to load - as this can be due to insufficient
resources on the system.
When we have portable binary configuration files, loading via
configfs, then this information is important to users.
Thanks
Mike
> Thanks,
> Mathieu
>
> > +
> > +The generator and reader programs can also be built directly, separately from
> > +the kernel build by using the 'Makefile.host' file. This allows native binaries
> > +to be created on the host machine rather than cross compiled version for the
> > +target.
> > +
> > +
> > +Binary Configuration File Format
> > +--------------------------------
> > +
> > +The file format is defined in the source file **coresight-config-file.h**
> > +
> > +The source reader and generator examples produce a binary of this format.
> > +
> > +This arrangement is reproduced below:-
> > +
> > +Overall File structure
> > +~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +::
> > +
> > + [cscfg_file_header] // Mandatory
> > + [CONFIG_ELEM] // Optional - one per file, if present, first element in file.
> > + [FEATURE_ELEM]* // Optional - multiple, defined by cscfg_file_header.nr_features
> > +
> > +File is invalid if both [CONFIG_ELEM] and [FEATURE_ELEM] are omitted.
> > +
> > +A file that contains only [FEATURE_ELEM] may be loaded, and the features used
> > +by subsequently loaded files with [CONFIG_ELEM] elements.
> > +
> > +Where [CONFIG_ELEM] is present, then **cscfg_file_header.nr_features** and
> > +**CONFIG_ELEM.nr_feat_refs** must have the same value.
> > +
> > +CONFIG_ELEM element
> > +~~~~~~~~~~~~~~~~~~~
> > +
> > +::
> > +
> > + [cscfg_file_elem_header] // header length value to end of feature strings.
> > + [cscfg_file_elem_str] // name of the configuration.
> > + [cscfg_file_elem_str] // description of configuration.
> > + [u16 value](nr_presets) // number of defined presets.
> > + [u32 value](nr_total_params) // total parameters defined by all used features.
> > + [u16 value](nr_feat_refs) // number of features referenced by the configuration
> > + [u64 values] * (nr_presets * nr_total_params) // the preset values.
> > + [cscfg_file_elem_str] * (nr_feat_refs) // the features used in the configurations.
> > +
> > +FEATURE_ELEM element
> > +~~~~~~~~~~~~~~~~~~~~
> > +
> > +::
> > +
> > + [cscfg_file_elem_header] // header length is total bytes to end of param structures.
> > + [cscfg_file_elem_str] // feature name.
> > + [cscfg_file_elem_str] // feature description.
> > + [u32 value](match_flags) // flags to associate the feature with a device.
> > + [u16 value](nr_regs) // number of registers.
> > + [u16 value](nr_params) // number of parameters.
> > + [cscfg_regval_desc struct] * (nr_regs) // register definitions
> > + [PARAM_ELEM] * (nr_params) // parameters definitions
> > +
> > +PARAM_ELEM element
> > +~~~~~~~~~~~~~~~~~~
> > +
> > +::
> > +
> > + [cscfg_file_elem_str] // parameter name.
> > + [u64 value](param_value] // initial value.
> > +
> > +Additional definitions.
> > +~~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +The following structures are defined in **coresight-config-file.h**
> > +
> > + * **struct cscfg_file_header** : This structure contains an initial magic number, the total
> > + length of the file, and the number of features in the file.
> > + * **struct cscfg_file_elem_header**: This defines the total length and type of a CONFIG_ELEM
> > + or a FEATURE_ELEM.
> > + * **struct cscfg_file_elem_str**: This defines a string and its length.
> > +
> > +The magic number in cscfg_file_header is defined as two bitfields::
> > +
> > + [31:8] Fixed magic number to identify file type.
> > + [7:0] Current file format version.
> > +
> > +The following defines determine the maximum overall file size and maximum individual
> > +string size::
> > +
> > + CSCFG_FILE_MAXSIZE // maximum overall file size.
> > + CSCFG_FILE_STR_MAXSIZE // maximum individual string size.
> > --
> > 2.17.1
> >
--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK
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