Message-ID: <Y6KDqe26J8RyoJIV@debian.me>
Date:   Wed, 21 Dec 2022 10:55:21 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Mike Leach <mike.leach@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Cc:     mathieu.poirier@...aro.org, suzuki.poulose@....com,
        acme@...nel.org, james.clark@....com,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 6/6] Documentation: coresight: docs for config load
 via configfs

On Mon, Dec 19, 2022 at 11:46:38PM +0000, Mike Leach wrote:
> diff --git a/Documentation/trace/coresight/coresight-config.rst b/Documentation/trace/coresight/coresight-config.rst
> index 6d5ffa6f7347..109053eb1b93 100644
> --- a/Documentation/trace/coresight/coresight-config.rst
> +++ b/Documentation/trace/coresight/coresight-config.rst
> @@ -141,11 +141,11 @@ Mount configfs as normal and the 'cs-syscfg' subsystem will appear::
>      $ ls /config
>      cs-syscfg  stp-policy
>  
> -This has two sub-directories::
> +This has two sub-directories, with the load and unload attribute files::
>  
>      $ cd cs-syscfg/
>      $ ls
> -    configurations  features
> +    configurations features load  unload
>  
>  The system has the configuration 'autofdo' built in. It may be examined as
>  follows::
> @@ -278,9 +278,16 @@ 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.
>  
> -An example of a custom configuration is found in ./samples/coresight.
> +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.
> +
> +
> +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 +296,187 @@ 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.

What config options (CONFIG_) are required for above to work?

> +
> +An example of a custom configuration module is found in './samples/coresight'.
> +
> +Using a Binary Configuration File
> +---------------------------------
> +
> +The './tools/coresight' directory contains example programs to generate and
> +read and print binary configuration files.
> +
> +Building the tools creates the 'coresight-cfg-file-gen' 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-example1.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. Alternatively, addition examples can be added to the

s/addition/additional/

> +'coresight-cfg-file-gen' program::
> +
> +    $ ./coresight-cfg-file-gen
> +    Coresight Configuration file Generator
> +
> +    Generating example1 example
> +    Generating example2 example
> +
> +The program 'coresight-cfg-file-read' can read back and print a configuration
> +binary. This is built using the file reader from the driver code
> +(coresight-config-file.c), which is copied over into './tools/coresight' at
> +build time.::
> +
> +    ./coresight-cfg-file-read example1.cscfg
> +    CoreSight Configuration file reader
> +    ============================================
> +
> +    Configuration 1
> +    Name:- autofdo3
> +    Description:-
> +    Setup ETMs with strobing for autofdo
> +    Supplied presets allow experimentation with mark-space ratio for various loads
> +
> +    Uses 1 features:-
> +    Feature-1: strobing
> +
> +    Provides 4 sets of preset values, 2 presets per set
> +    set[0]: 0x7d0, 0x64,
> +    set[1]: 0x7d0, 0x3e8,
> +    set[2]: 0x7d0, 0x1388,
> +    set[3]: 0x7d0, 0x2710,
> +
> +    ============================================
> +    File contains no features
> +
> +There are additional attributes in the cs-syscfg directory - load and
> +unload 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 features  load  unload
> +    $ cat example1.cscfg > /config/cs-syscfg/load
> +    $ ls /config/cs-syscfg/configurations/
> +    autofdo  autofdo3
> +
> +To unload, use the same file in the unload attribute::
> +
> +    $ cat example1.cscfg > /config/cs-syscfg/unload
> +    ls /config/cs-syscfg/configurations/
> +    autofdo
> +
> +
> +
> +Binary Configuration File Format
> +--------------------------------
> +
> +The file format is defined in the source file **coresight-config-file.h**

Use single-quote for identifier names for consistency here.

> +
> +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 - multiple, defined by cscfg_file_header.nr_configs
> +   [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.
> +
> +Element Name Strings
> +~~~~~~~~~~~~~~~~~~~~
> +
> +Configuration name strings are required to consist of alphanumeric characters and '_' only. Other special characters are not permitted.
> +
> +::
> +   my_config_2          // is a valid name.
> +   this-bad-config#5    // this will not work

Instead of using code-block for name examples, what about "... For
example, foo_bar is a valid name where as foo-bar# is not."?

> +
> +This is in order to comply with the requirements of the perf command line.
> +
> +It is recommended that Feature and Parameter names use the same convention to allow for future enhancements to the command line syntax.
> +
> +CONFIG_ELEM element
> +~~~~~~~~~~~~~~~~~~~
> +
> +::
> +
> +   [cscfg_file_elem_header]                // header length value to end of feature strings.
> +   [cscfg_file_elem_str]                   // name of the configuration.
> +                                           // (see element string name requirements)
> +   [cscfg_file_elem_str]                   // description of configuration.
> +   [u16 value](nr_presets)                 // number of defined sets presets values.
> +   [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)  // names of 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.
> +~~~~~~~~~~~~~~~~~~~~~~~

Trim trailing period for section names

> +
> +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 configurations and 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.

Again, for consistency, wrap identifier names in single-quotes.

> +
> +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.

For parameter lists in elements, use bullet lists instead.

> +
> +Load Dependencies.
> +~~~~~~~~~~~~~~~~~~

Trim trailing period for section names.
> +
> +Files may be unloaded only in the strict reverse order of loading. This is enforced by the
> +configuration system.
> +
> +This is to ensure that any load dependencies are maintained.
> +
> +A configuration file that contains a CONFIG_ELEM that references named features "feat_A" and "feat_B" will load only if either:-
> +a) "feat_A" and/or "feat_B" has been loaded previously, or are present as built-in / module loaded features.
> +b) "feat_A" and/or "feat_B" are declared as FEAT_ELEM in the same file as the CONFIG_ELEM.

Separate the preceding paragraph and the list with a blank line in order
for the list to be rendered as list.

Thanks.

-- 
An old man doll... just what I always wanted! - Clara

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