[PATCH v5 6/6] Documentation: coresight: docs for config load via configfs

[Mike Leach]

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.

Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Signed-off-by: Mike Leach <mike.leach@xxxxxxxxxx>
---
 .../trace/coresight/coresight-config.rst      | 202 +++++++++++++++++-
 1 file changed, 195 insertions(+), 7 deletions(-)

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.
+
+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
+'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**
+
+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
+
+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.
+~~~~~~~~~~~~~~~~~~~~~~~
+
+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.
+
+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.
+
+Load Dependencies.
+~~~~~~~~~~~~~~~~~~
+
+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.
+
+Files that contain features or configurations with the same names as those already loaded will fail to load.
-- 
2.17.1