[PATCH v8-RESEND 19/33] dyndbg-doc: add classmap info to howto

[Jim Cromie <jim.cromie@gmail.com>]

Describe the 3 API macros providing dynamic_debug's classmaps

DYNDBG_CLASSMAP_DEFINE - create, exports a module's classmap
DYNDBG_CLASSMAP_USE    - refer to exported map
DYNDBG_CLASSMAP_PARAM  - bind control param to the classmap
DYNDBG_CLASSMAP_PARAM_REF + use module's storage - __drm_debug

cc: linux-doc@vger.kernel.org
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
v5 adjustments per Randy Dunlap
v7 checkpatch fixes
v8 more
---
 .../admin-guide/dynamic-debug-howto.rst       | 63 ++++++++++++++++++-
 1 file changed, 62 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index 6a8ce5a34382..742eb4230c6e 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -225,7 +225,6 @@ the ``p`` flag has meaning, other flags are ignored.
 Note the regexp ``^[-+=][fslmpt_]+$`` matches a flags specification.
 To clear all flags at once, use ``=_`` or ``-fslmpt``.
 
-
 Debug messages during Boot Process
 ==================================
 
@@ -375,3 +374,65 @@ just a shortcut for ``print_hex_dump(KERN_DEBUG)``.
 For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is
 its ``prefix_str`` argument, if it is constant string; or ``hexdump``
 in case ``prefix_str`` is built dynamically.
+
+Dynamic Debug classmaps
+=======================
+
+Dyndbg allows selection/grouping of *prdbg* callsites using structural
+info: module, file, function, line.  Classmaps allow authors to add
+their own domain-oriented groupings using class-names.  Classmaps are
+exported, so they referencable from other modules.
+
+  # enable classes individually
+  :#> ddcmd class DRM_UT_CORE +p
+  :#> ddcmd class DRM_UT_KMS +p
+  # or more selectively
+  :#> ddcmd class DRM_UT_CORE module drm +p
+
+The "class FOO" syntax protects class'd prdbgs from generic overwrite::
+
+  # IOW this doesn't wipe any DRM.debug settings
+  :#> ddcmd -p
+
+To support the DRM.debug parameter, DYNDBG_CLASSMAP_PARAM* updates all
+classes in a classmap, mapping param-bits 0..N onto the classes:
+DRM_UT_<*> for the DRM use-case.
+
+Dynamic Debug Classmap API
+==========================
+
+DYNDBG_CLASSMAP_DEFINE - modules use this to create classmaps, naming
+each of the classes (stringified enum-symbols: "DRM_UT_<*>"), and
+type, and mapping the class-names to consecutive _class_ids.
+
+By doing so, modules tell dyndbg that they have prdbgs with those
+class_ids, and they authorize dyndbg to accept "class FOO" for the
+module defining the classmap, and its contained classnames.
+
+DYNDBG_CLASSMAP_USE - drm drivers invoke this to ref the CLASSMAP that
+drm DEFINEs.  This shares the classmap definition, and authorizes
+dyndbg to apply changes to the user module's class'd pr_debugs.  It
+also tells dyndbg how to initialize the user's prdbgs at modprobe,
+based upon the current setting of the parent's controlling param.
+
+There are 2 types of classmaps:
+
+ DD_CLASS_TYPE_DISJOINT_BITS: classes are independent, like DRM.debug
+ DD_CLASS_TYPE_LEVEL_NUM: classes are relative, ordered (V3 > V2)
+
+DYNDBG_CLASSMAP_PARAM - modelled after module_param_cb, it refers to a
+DEFINEd classmap, and associates it to the param's data-store.  This
+state is then applied to DEFINEr and USEr modules when they're modprobed.
+
+This interface also enforces the DD_CLASS_TYPE_LEVEL_NUM relation
+amongst the contained classnames; all classes are independent in the
+control parser itself.
+
+Modules or module-groups (drm & drivers) can define multiple
+classmaps, as long as they share the limited 0..62 per-module-group
+_class_id range, without overlap.
+
+``#define DEBUG`` will enable all pr_debugs in scope, including any
+class'd ones.  This won't be reflected in the PARAM readback value,
+but the class'd pr_debug callsites can be forced off by toggling the
+classmap-kparam all-on then all-off.
-- 
2.45.0