[PATCH v5 21/22] dyndbg-doc: add classmap info to howto

From: Jim Cromie
Date: Tue Aug 01 2023 - 13:05:39 EST

Add some basic info on classmap usage and api

Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
.../admin-guide/dynamic-debug-howto.rst | 64 ++++++++++++++++++-
1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
index 8dc668cc1216..b8d2a7235cbb 100644
--- a/Documentation/admin-guide/dynamic-debug-howto.rst
+++ b/Documentation/admin-guide/dynamic-debug-howto.rst
@@ -224,7 +224,6 @@ the ``p`` flag has meaning, other flags are ignored.
Note the regexp ``^[-+=][flmpt_]+$`` matches a flags specification.
To clear all flags at once, use ``=_`` or ``-flmpt``.

Debug messages during Boot Process

@@ -374,3 +373,66 @@ 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 generally selects *prdbg* callsites using structural info:
+module, file, function, line. Using classmaps, user modules can
+organize/select pr_debug()s as they like.
+- classes coordinates/spans multiple modules
+- complements the mod,file,func attrs
+- keeps pr_debug's 0-off-cost JUMP_LABEL goodness
+- isolates each from other class'd and un-class'd pr_debugs()
+ (one doesn't intermix 2 clients' bank accounts)
+ # IOW this doesn't change DRM.debug settings
+ #> echo -p > /proc/dynamic_debug/control
+ # change the classes by naming them explicitly (no wildcard here)
+ #> echo class DRM_UT_CORE +p > /proc/dynamic_debug/control
+To support DRM.debug (/sys/module/drm/parameters/debug), dyndbg
+provides DYNDBG_CLASSMAP_PARAM*. It maps the categories/classes:
+DRM_UT_CORE.. to bits 0..N, allowing to set all classes at once.
+Dynamic Debug Classmap API
+DYNDBG_CLASSMAP_DEFINE - modules create CLASSMAPs, naming the classes
+and type, and mapping the class-names to consecutive _class_ids. By
+doing so, they tell dyndbg that they are using those class_ids, and
+authorize dyndbg to manipulate the callsites by their class-names.
+Its expected that client modules will follow the DRM.debug model:
+1. define their debug-classes using an enum type, where the enum
+symbol and its integer value define both the classnames and class-ids.
+2. use or macro-wrap __pr_debug_cls(ENUM_VAL, "hello world\n")
+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)
+Both these classmap-types use the class-names/ENUM_VALs to validate
+commands into >control.
+DYNDBG_CLASSMAP_PARAM - refers to a DEFINEd classmap, exposing the set
+of defined classes to manipulation as a group. This interface
+enforces the relatedness of classes of DD_CLASS_TYPE_LEVEL_NUM typed
+classmaps; all classes are independent in the >control parser itself.
+DYNDBG_CLASSMAP_USE - drm drivers use the CLASSMAP that drm DEFINEs.
+This shares the classmap definition, authorizes coordinated changes
+amongst the CLASSMAP DEFINEr and multiple USErs, and tells dyndbg
+how to initialize the user's prdbgs at modprobe.
+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 (__pr_debug_cls(id,fmt..)). This won't be reflected in
+the PARAM readback value, but the pr_debug callsites can be toggled
+into agreement with the param.