[PATCH v6 6/6] Documentation: coresight: docs for config load via configfs
From: Mike Leach
Date: Thu May 11 2023 - 02:54:07 EST
Add documentation covering the configfs updates that allow
configuration tables to be loaded and unloaded via configfs,
along with the demonstration programs in tools/coresight.
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Signed-off-by: Mike Leach <mike.leach@xxxxxxxxxx>
---
.../trace/coresight/coresight-config.rst | 265 ++++++++++++++++--
1 file changed, 242 insertions(+), 23 deletions(-)
diff --git a/Documentation/trace/coresight/coresight-config.rst b/Documentation/trace/coresight/coresight-config.rst
index 6d5ffa6f7347..fe50bfaada5e 100644
--- a/Documentation/trace/coresight/coresight-config.rst
+++ b/Documentation/trace/coresight/coresight-config.rst
@@ -109,20 +109,20 @@ Operation
The following steps take place in the operation of a configuration.
-1) In this example, the configuration is 'autofdo', which has an
- associated feature 'strobing' that works on ETMv4 CoreSight Devices.
+1) In this example, the configuration is ``autofdo``, which has an
+ associated feature ``strobing`` that works on ETMv4 CoreSight Devices.
-2) The configuration is enabled. For example 'perf' may select the
+2) The configuration is enabled. For example ``perf`` may select the
configuration as part of its command line::
perf record -e cs_etm/autofdo/ myapp
- which will enable the 'autofdo' configuration.
+ which will enable the ``autofdo`` configuration.
3) perf starts tracing on the system. As each ETMv4 that perf uses for
trace is enabled, the configuration manager will check if the ETMv4
has a feature that relates to the currently active configuration.
- In this case 'strobing' is enabled & programmed into the ETMv4.
+ In this case ``strobing`` is enabled & programmed into the ETMv4.
4) When the ETMv4 is disabled, any registers marked as needing to be
saved will be read back.
@@ -136,18 +136,18 @@ Viewing Configurations and Features
The set of configurations and features that are currently loaded into the
system can be viewed using the configfs API.
-Mount configfs as normal and the 'cs-syscfg' subsystem will appear::
+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
+The system has the configuration ``autofdo`` built in. It may be examined as
follows::
$ cd configurations/
@@ -162,7 +162,7 @@ follows::
$ 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
@@ -170,7 +170,7 @@ 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
+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
@@ -210,18 +210,18 @@ Using Configurations in perf
============================
The configurations loaded into the CoreSight configuration management are
-also declared in the perf 'cs_etm' event infrastructure so that they can
+also declared in the perf ``cs_etm`` event infrastructure so that they can
be selected when running trace under perf::
$ ls /sys/devices/cs_etm
cpu0 cpu2 events nr_addr_filters power subsystem uevent
cpu1 cpu3 format perf_event_mux_interval_ms sinks type
-The key directory here is 'events' - a generic perf directory which allows
+The key directory here is ``events`` - a generic perf directory which allows
selection on the perf command line. As with the sinks entries, this provides
a hash of the configuration name.
-The entry in the 'events' directory uses perfs built in syntax generator
+The entry in the ``events`` directory uses perfs built in syntax generator
to substitute the syntax for the name when evaluating the command::
$ ls events/
@@ -229,7 +229,7 @@ to substitute the syntax for the name when evaluating the command::
$ cat events/autofdo
configid=0xa7c3dddd
-The 'autofdo' configuration may be selected on the perf command line::
+The ``autofdo`` configuration may be selected on the perf command line::
$ perf record -e cs_etm/autofdo/u --per-thread <application>
@@ -246,7 +246,7 @@ 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.
+In a configuration there are ``enable`` and ``preset`` files.
To enable a configuration for use with sysfs::
@@ -256,13 +256,13 @@ To enable a configuration for use with sysfs::
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::
+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.
+<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.
@@ -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 configuration table
+through 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 +296,218 @@ 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 selected in KConfig.
+(select ``CONFIG_SAMPLE_CORESIGHT_SYSCFG``).
+
+An example of a custom configuration module is found in ``./samples/coresight``.
+
+Using a Configuration Table File
+--------------------------------
+
+The ``./tools/coresight`` directory contains example programs to generate and
+read and print binary configuration table 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, additional 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 tables.
+
+To load, 'cat' the table file into the load attribute::
+
+ $ ls /config/cs-syscfg
+ configurations features load show_last_load unload
+ $ cat example1.cscfg > /config/cs-syscfg/load
+ $ ls /config/cs-syscfg/configurations/
+ autofdo autofdo3
+
+As described above, in order to respect configuration dependencies, unload
+order is scrictly enforced to be the reverse of load order.
+
+``unload`` can be used to unload the last loaded configuration, but only
+if this was loaded using configfs.
+
+To unload, the *load name* of the configuration is written to ``unload``.
+This load name is the name of the first configuration in the table, or if no
+configurations, the name of the first feature.
+
+This name can be read either as described above, or by reading the
+``show_last_load`` attribute to obtain the details of the last loaded
+configuration::
+
+ $ cat /config/cs-syscfg/show_last_load
+ load name: autofdo3
+ load type: configfs dynamic load
+ (configurations: autofdo3 )
+ (features: None )
+
+Once this is known then unload by::
+
+ $ echo autofdo3 > /config/cs-syscfg/unload
+ ls /config/cs-syscfg/configurations/
+ autofdo
+
+Load and unload cannot be done if trace is in progress using a configuration.
+
+Unload will fail if the last loaded item was not a configfs dynamic loaded file.
+When using ``show_last_load`` a non configfs item will show::
+
+ cat /config/cs-syscfg/show_last_load
+ load name: [Not Set]
+ load type: Built in driver
+
+
+
+CoreSight Configuration Table Format
+------------------------------------
+
+The file format is defined in the source file ``coresight-config-table.h``
+
+The source reader and generator examples use/produce a table in this format,
+as a binary file.
+
+This arrangement is reproduced below:-
+
+Overall Table structure
+~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ [cscfg_table_header] // Mandatory
+ [CONFIG_ELEM]* // Optional - multiple, defined by cscfg_table_header.nr_configs
+ [FEATURE_ELEM]* // Optional - multiple, defined by cscfg_table_header.nr_features
+
+Table is invalid if both [CONFIG_ELEM] and [FEATURE_ELEM] are omitted.
+
+A table 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.
+
+For example ``my_config_2`` is a valid name, while ``this-bad-config#5`` 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_table_elem_header] // header length value to end of feature strings.
+ [cscfg_table_elem_str] // name of the configuration.
+ // (see element string name requirements)
+ [cscfg_table_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_table_elem_str] * (nr_feat_refs) // names of features used in the configurations.
+
+FEATURE_ELEM element
+~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ [cscfg_table_elem_header] // header length is total bytes to end of param structures.
+ [cscfg_table_elem_str] // feature name.
+ [cscfg_table_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_table_elem_str] // parameter name.
+ [u64 value](param_value) // initial value.
+
+Additional definitions
+~~~~~~~~~~~~~~~~~~~~~~
+
+The following structures are defined in ``coresight-config-file.h``
+
+ * ``struct cscfg_table_header`` : This structure contains an initial magic number, the total
+ length of the table, and the number of configurations and features in the table.
+ * ``struct cscfg_table_elem_header``: This defines the total length and type of a CONFIG_ELEM
+ or a FEATURE_ELEM.
+ * ``struct cscfg_table_elem_str``: This defines a string and its length.
+
+The magic number in cscfg_table_header is defined as two bitfields::
+
+ [31:8] Fixed magic number to identify table type.
+ [7:0] Current table format version.
+
+The following defines determine the maximum overall table size and maximum individual
+string size
+
+ * ``CSCFG_TABLE_MAXSIZE`` : maximum overall table size.
+ * ``CSCFG_TABLE_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 table 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 table as the CONFIG_ELEM.
+
+Tables that contain features or configurations with the same names as those already loaded will fail to load.
--
2.17.1