Subject: Re: [PATCH v2 6/6] Documentation: coresight: docs for config load via configfs

From: Mathieu Poirier <[email-masked]>
Date: Thu, 13 Jan 2022 11:15:57 -0700

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 <[email-masked]>
> ---
>  .../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.

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
> 

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