[PATCH v10 23/38] dyndbg-API: replace DECLARE_DYNDBG_CLASSMAP

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

DECLARE_DYNDBG_CLASSMAP had a flaw: multiple invocations across both
core and driver modules broke the K&R "define once, refer afterwards"
principle, causing boot-time parameter propagation failures.

Replace it with an explicit client-server model:
- DYNAMIC_DEBUG_CLASSMAP_DEFINE: invoked once in the core module, creating
  and exporting the classmap.
- DYNAMIC_DEBUG_CLASSMAP_USE: invoked across driver/helper modules,
  placing a reference record into the __dyndbg_class_users section.

At module load time, dyndbg scans __dyndbg_class_users, resolves the
reference to the parent classmap, finds the associated controlling
kernel parameter, and automatically applies the initial bitmap to the
loading module.

Fixes: aad0214f3026 ("dyndbg: add DECLARE_DYNDBG_CLASSMAP macro")
Cc: linux-doc@vger.kernel.org
Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
v10:
. pass init_bits computed from (_DPRINTK_FLAGS_DEFAULT & _DPRINTK_FLAGS_PRINT) in
  ddebug_sync_classbits() to properly disable -DDEBUG callsites.
---
 include/asm-generic/dyndbg.lds.h |   6 +-
 include/linux/dynamic_debug.h    | 164 ++++++++++++++++++++++++++++----
 kernel/module/main.c             |   3 +
 lib/Kconfig.debug                |  24 ++++-
 lib/Makefile                     |   3 +
 lib/dynamic_debug.c              | 197 +++++++++++++++++++++++++++++++++++++--
 lib/test_dynamic_debug.c         | 131 ++++++++++++++++++++------
 lib/test_dynamic_debug_submod.c  |  14 +++
 8 files changed, 485 insertions(+), 57 deletions(-)

diff --git a/include/asm-generic/dyndbg.lds.h b/include/asm-generic/dyndbg.lds.h
index ec661f9f3793..0ffc9cde4377 100644
--- a/include/asm-generic/dyndbg.lds.h
+++ b/include/asm-generic/dyndbg.lds.h
@@ -5,7 +5,8 @@
 #include <asm-generic/bounded_sections.lds.h>
 #define DYNDBG_SECTIONS()						\
 	BOUNDED_SECTION_BY(__dyndbg_descs, ___dyndbg_descs)		\
-	BOUNDED_SECTION_BY(__dyndbg_class_maps, ___dyndbg_class_maps)
+	BOUNDED_SECTION_BY(__dyndbg_class_maps, ___dyndbg_class_maps)	\
+	BOUNDED_SECTION_BY(__dyndbg_class_users, ___dyndbg_class_users)
 
 #define MOD_DYNDBG_SECTIONS()						\
 	__dyndbg_descs 0 : ALIGN(8) {					\
@@ -13,6 +14,9 @@
 	}								\
 	__dyndbg_class_maps 0 : ALIGN(8) {				\
 		KEEP(*(__dyndbg_class_maps))				\
+	}								\
+	__dyndbg_class_users 0 : ALIGN(8) {				\
+		KEEP(*(__dyndbg_class_users))				\
 	}
 
 #endif /* __ASM_GENERIC_DYNDBG_LDS_H */
diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index bf6039191fa7..61f9fd4aa7af 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -83,19 +83,30 @@ enum ddebug_class_map_type {
 	 */
 };
 
+/*
+ * map @class_names 0..N to consecutive constants starting at @base.
+ */
 struct ddebug_class_map {
-	struct module *mod;	/* NULL for builtins */
-	const char *mod_name;	/* needed for builtins */
+	const struct module *mod;	/* NULL for builtins */
+	const char *mod_name;		/* needed for builtins */
 	const char **class_names;
 	const int length;
 	const int base;		/* index of 1st .class_id, allows split/shared space */
 	enum ddebug_class_map_type map_type;
-};
+} __aligned(8);
+
+struct ddebug_class_user {
+	const char *mod_name;
+	struct ddebug_class_map *map;
+	const int offset;	/* offset from map->base */
+} __aligned(8);
 
 /*
- * @_ddebug_info: gathers module/builtin dyndbg_* __sections together.
+ * @_ddebug_info: gathers module/builtin __dyndbg_<T> __sections
+ * together, each is a vec_<T>: a struct { struct T start[], int len }.
+ *
  * For builtins, it is used as a cursor, with the inner structs
- * marking sub-vectors of the builtin __sections in DATA.
+ * marking sub-vectors of the builtin __sections in DATA_DATA
  */
 struct _ddebug_descs {
 	struct _ddebug *start;
@@ -107,10 +118,16 @@ struct _ddebug_class_maps {
 	unsigned int len;
 };
 
+struct _ddebug_class_users {
+	struct ddebug_class_user *start;
+	int len;
+};
+
 struct _ddebug_info {
 	const char *mod_name;
 	struct _ddebug_descs descs;
 	struct _ddebug_class_maps maps;
+	struct _ddebug_class_users users;
 };
 
 struct ddebug_class_param {
@@ -129,17 +146,86 @@ struct ddebug_class_param {
 #if defined(CONFIG_DYNAMIC_DEBUG) || \
 	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 
+/*
+ * dyndbg classmaps is modelled closely upon drm.debug:
+ *
+ *  1. run-time control via sysfs node (api/abi)
+ *  2. each bit 0..N controls a single "category"
+ *  3. a pr_debug can have only 1 category, not several.
+ *  4. "kind" is a compile-time constant: 0..N or BIT() thereof
+ *  5. macro impls - give compile-time resolution or fail.
+ *
+ * dyndbg classmaps design axioms/constraints:
+ *
+ *  . optimizing compilers use 1-5 above, so preserve them.
+ *  . classmaps.class_id *is* the category.
+ *  . classmap definers/users are modules.
+ *  . every user wants 0..N
+ *  . 0..N exposes as ABI
+ *  . no 1 use-case wants N > 32, 16 is more usable
+ *  . N <= 64 in *all* cases
+ *  . modules/subsystems make category/classmap decisions
+ *  . ie an enum: DRM has DRM_UT_CORE..DRM_UT_DRMRES
+ *  . some categories are exposed to user: ABI
+ *  . making modules change their numbering is bogus, avoid if possible
+ *
+ * We can solve for all these at once:
+ *  A: map class-names to a .class_id range at compile-time
+ *  B: allow only "class NAME" changes to class'd callsites at run-time
+ *  C: users/modules must manage 0..62 hardcoded .class_id range limit.
+ *  D: existing pr_debugs get CLASS_DFLT=63
+ *
+ * By mapping class-names at >control to class-ids underneath, and
+ * responding only to class-names DEFINEd or USEd by the module, we
+ * can private-ize the class-id, and adjust class'd pr_debugs only by
+ * their names.
+ *
+ * This give us:
+ *  E: class_ids without classnames are unreachable
+ *  F: user modules opt-in by DEFINEing a classmap and/or USEing another
+ *
+ * Multi-classmap modules/groups are supported, if the classmaps share
+ * the class_id space [0..62] without overlap/conflict.
+ *
+ * NOTE: Due to the integer class_id, this api cannot disallow these:
+ * __pr_debug_cls(0, "fake CORE msg");  works only if a classmap maps 0.
+ * __pr_debug_cls(22, "no such class"); compiles but is not reachable
+ */
+
 /**
- * DECLARE_DYNDBG_CLASSMAP - declare classnames known by a module
- * @_var:   a struct ddebug_class_map, passed to module_param_cb
- * @_maptype: enum ddebug_class_map_type, chooses bits/verbose
- * @_base:  offset of 1st class-name. splits .class_id space
- * @classes: class-names used to control class'd prdbgs
+ * DYNAMIC_DEBUG_CLASSMAP_DEFINE - define debug classes used by a module.
+ * @_var:   name of the classmap, exported for other modules coordinated use.
+ * @_mapty: enum ddebug_class_map_type: 0:DISJOINT - independent, 1:LEVEL - v2>v1
+ * @_base:  reserve N classids starting at _base, to split 0..62 classid space
+ * @classes: names of the N classes.
+ *
+ * This tells dyndbg what class_ids the module is using: _base..+N, by
+ * mapping names onto them.  This qualifies "class NAME" >controls on
+ * the defining module, ignoring unknown names.
+ */
+#define DYNAMIC_DEBUG_CLASSMAP_DEFINE(_var, _mapty, _base, ...)		\
+	static const char *_var##_classnames[] = { __VA_ARGS__ };	\
+	extern struct ddebug_class_map _var;				\
+	struct ddebug_class_map __aligned(8) __used			\
+		__section("__dyndbg_class_maps") _var = {		\
+		.mod = THIS_MODULE,					\
+		.mod_name = DDEBUG_MODNAME,				\
+		.base = (_base),					\
+		.map_type = (_mapty),					\
+		.length = ARRAY_SIZE(_var##_classnames),		\
+		.class_names = _var##_classnames,			\
+	};								\
+	EXPORT_SYMBOL(_var)
+
+/*
+ * XXX: keep this until DRM adapts to use the DEFINE/USE api, it
+ * differs from DYNAMIC_DEBUG_CLASSMAP_DEFINE by the lack of the
+ * extern/EXPORT on the struct init, and cascading thinkos.
  */
 #define DECLARE_DYNDBG_CLASSMAP(_var, _maptype, _base, ...)		\
 	static const char *_var##_classnames[] = { __VA_ARGS__ };	\
 	static struct ddebug_class_map __aligned(8) __used		\
-		__section("__dyndbg_class_maps") _var = {			\
+		__section("__dyndbg_class_maps") _var = {		\
 		.mod = THIS_MODULE,					\
 		.mod_name = DDEBUG_MODNAME,				\
 		.base = _base,						\
@@ -148,6 +234,44 @@ struct ddebug_class_param {
 		.length = __DDEBUG_ARRAY_SIZE(_var##_classnames),	\
 	}
 
+/**
+ * DYNAMIC_DEBUG_CLASSMAP_USE - refer to a classmap, DEFINEd elsewhere.
+ * @_var: name of the exported classmap var
+ *
+ * This tells dyndbg that the module has prdbgs with classids defined
+ * in the named classmap.  This qualifies "class NAME" >controls on
+ * the user module, and ignores unknown names. This is a wrapper for
+ * DYNAMIC_DEBUG_CLASSMAP_USE_() with a base offset of 0.
+ */
+#define DYNAMIC_DEBUG_CLASSMAP_USE(_var) \
+	DYNAMIC_DEBUG_CLASSMAP_USE_(_var, 0)
+
+/**
+ * DYNAMIC_DEBUG_CLASSMAP_USE_ - refer to a classmap with a manual offset.
+ * @_var:   name of the exported classmap var to use.
+ * @_offset:  an integer offset to add to the class IDs of the used map.
+ *
+ * This is an extended version of DYNAMIC_DEBUG_CLASSMAP_USE(). It should
+ * only be used to resolve class ID conflicts when a module uses multiple
+ * classmaps that have overlapping ID ranges.
+ *
+ * The final class IDs for the used map will be calculated as:
+ * original_map_base + class_index + @_offset.
+ */
+#define DYNAMIC_DEBUG_CLASSMAP_USE_(_var, _offset)			\
+	extern struct ddebug_class_map _var;				\
+	static_assert((_offset) >= 0 && (_offset) < _DPRINTK_CLASS_DFLT, \
+		      "classmap use offset must be in 0..62");          \
+	extern struct ddebug_class_user __aligned(8)			\
+		__PASTE(_var ## _, __KBUILD_MODNAME);			\
+	struct ddebug_class_user __aligned(8) __used			\
+		__section("__dyndbg_class_users")			\
+		__PASTE(_var ## _, __KBUILD_MODNAME) = {		\
+		.mod_name = DDEBUG_MODNAME,				\
+		.map = &(_var),						\
+		.offset = _offset					\
+	}
+
 extern __printf(2, 3)
 void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...);
 
@@ -309,12 +433,18 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 				   KERN_DEBUG, prefix_str, prefix_type,	\
 				   rowsize, groupsize, buf, len, ascii)
 
-/* for test only, generally expect drm.debug style macro wrappers */
-#define __pr_debug_cls(cls, fmt, ...) do {			\
+/*
+ * This is the "model" class variant of pr_debug.  It is not really
+ * intended for direct use; I'd encourage DRM-style drm_dbg_<T>
+ * macros for the interface, along with an enum for the <T>
+ *
+ * __printf(2, 3) would apply.
+ */
+#define __pr_debug_cls(cls, fmt, ...) ({			\
 	BUILD_BUG_ON_MSG(!__builtin_constant_p(cls),		\
 			 "expecting constant class int/enum");	\
 	dynamic_pr_debug_cls(cls, fmt, ##__VA_ARGS__);		\
-	} while (0)
+})
 
 #else /* !(CONFIG_DYNAMIC_DEBUG || (CONFIG_DYNAMIC_DEBUG_CORE && DYNAMIC_DEBUG_MODULE)) */
 
@@ -322,6 +452,9 @@ void __dynamic_ibdev_dbg(struct _ddebug *descriptor,
 #include <linux/errno.h>
 #include <linux/printk.h>
 
+#define DYNAMIC_DEBUG_CLASSMAP_DEFINE(_var, _mapty, _base, ...)
+#define DYNAMIC_DEBUG_CLASSMAP_USE(_var)
+#define DYNAMIC_DEBUG_CLASSMAP_USE_(_var, _offset)
 #define DEFINE_DYNAMIC_DEBUG_METADATA(name, fmt)
 #define DYNAMIC_DEBUG_BRANCH(descriptor) false
 #define DECLARE_DYNDBG_CLASSMAP(...)
@@ -368,8 +501,7 @@ static inline int param_set_dyndbg_classes(const char *instr, const struct kerne
 static inline int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp)
 { return 0; }
 
-#endif
-
+#endif /* !CONFIG_DYNAMIC_DEBUG_CORE */
 
 extern const struct kernel_param_ops param_ops_dyndbg_classes;
 
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 852cce2c5113..abf0c6991f66 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2791,6 +2791,9 @@ static int find_module_sections(struct module *mod, struct load_info *info)
 	mod->dyndbg_info.maps.start = section_objs(info, "__dyndbg_class_maps",
 						   sizeof(*mod->dyndbg_info.maps.start),
 						   &mod->dyndbg_info.maps.len);
+	mod->dyndbg_info.users.start = section_objs(info, "__dyndbg_class_users",
+						   sizeof(*mod->dyndbg_info.users.start),
+						   &mod->dyndbg_info.users.len);
 #endif
 
 	return 0;
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c3f448f3b8f1..2abf28d6d063 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -3138,12 +3138,26 @@ config TEST_STATIC_KEYS
 	  If unsure, say N.
 
 config TEST_DYNAMIC_DEBUG
-	tristate "Test DYNAMIC_DEBUG"
-	depends on DYNAMIC_DEBUG
+	tristate "Build test-dynamic-debug module"
+	depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE
 	help
-	  This module registers a tracer callback to count enabled
-	  pr_debugs in a 'do_debugging' function, then alters their
-	  enablements, calls the function, and compares counts.
+	  This module exercises/demonstrates dyndbg's classmap API, by
+	  creating 2 classes: a DISJOINT classmap (supporting DRM.debug)
+	  and a LEVELS/VERBOSE classmap (like verbose2 > verbose1).
+
+	  If unsure, say N.
+
+config TEST_DYNAMIC_DEBUG_SUBMOD
+	tristate "Build test-dynamic-debug submodule"
+	default m
+	depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE
+	depends on TEST_DYNAMIC_DEBUG
+	help
+	  This sub-module uses a classmap defined and exported by the
+	  parent module, recapitulating drm & driver's shared use of
+	  drm.debug to control enabled debug-categories.
+	  It is tristate, independent of parent, to allow testing all
+	  proper combinations of parent=y/m submod=y/m.
 
 	  If unsure, say N.
 
diff --git a/lib/Makefile b/lib/Makefile
index dfab958327c5..9cdf0a430f5f 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -85,6 +85,7 @@ obj-$(CONFIG_TEST_RHASHTABLE) += test_rhashtable.o
 obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_keys.o
 obj-$(CONFIG_TEST_STATIC_KEYS) += test_static_key_base.o
 obj-$(CONFIG_TEST_DYNAMIC_DEBUG) += test_dynamic_debug.o
+obj-$(CONFIG_TEST_DYNAMIC_DEBUG_SUBMOD) += test_dynamic_debug_submod.o
 
 obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o
 ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_KASAN),yy)
@@ -206,6 +207,8 @@ obj-$(CONFIG_ARCH_NEED_CMPXCHG_1_EMU) += cmpxchg-emu.o
 obj-$(CONFIG_DYNAMIC_DEBUG_CORE) += dynamic_debug.o
 #ensure exported functions have prototypes
 CFLAGS_dynamic_debug.o := -DDYNAMIC_DEBUG_MODULE
+CFLAGS_test_dynamic_debug.o := -DDYNAMIC_DEBUG_MODULE
+CFLAGS_test_dynamic_debug_submod.o := -DDYNAMIC_DEBUG_MODULE
 
 obj-$(CONFIG_SYMBOLIC_ERRNAME) += errname.o
 
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 03dc35af4faa..566c3860d7bf 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -29,6 +29,7 @@
 #include <linux/string_helpers.h>
 #include <linux/uaccess.h>
 #include <linux/dynamic_debug.h>
+
 #include <linux/debugfs.h>
 #include <linux/slab.h>
 #include <linux/jump_label.h>
@@ -43,6 +44,8 @@ extern struct _ddebug __start___dyndbg_descs[];
 extern struct _ddebug __stop___dyndbg_descs[];
 extern struct ddebug_class_map __start___dyndbg_class_maps[];
 extern struct ddebug_class_map __stop___dyndbg_class_maps[];
+extern struct ddebug_class_user __start___dyndbg_class_users[];
+extern struct ddebug_class_user __stop___dyndbg_class_users[];
 
 struct ddebug_table {
 	struct list_head link;
@@ -160,20 +163,39 @@ static void v3pr_info_dq(const struct ddebug_query *query, const char *msg)
 	     (_i) < (_box)->_vec.len;			\
 	     (_i)++, (_sp)++)		/* { block } */
 
-static struct ddebug_class_map *ddebug_find_valid_class(struct ddebug_table const *dt,
-							 const char *class_string,
+#define v2pr_di_info(di_p, msg_p, ...)					\
+({									\
+	struct _ddebug_info const *_di = di_p;				\
+	v2pr_info(msg_p "module:%s nd:%d nc:%d nu:%d\n", ##__VA_ARGS__, \
+		  _di->mod_name, _di->descs.len, _di->maps.len,         \
+		  _di->users.len);                                      \
+})
+
+static struct ddebug_class_map *ddebug_find_valid_class(struct _ddebug_info const *di,
+							 const char *query_class,
 							 int *class_id)
 {
 	struct ddebug_class_map *map;
+	struct ddebug_class_user *cli;
 	int i, idx;
 
-	for_subvec(i, map, &dt->info, maps) {
-		idx = match_string(map->class_names, map->length, class_string);
+	for_subvec(i, map, di, maps) {
+		idx = match_string(map->class_names, map->length, query_class);
 		if (idx >= 0) {
+			v2pr_di_info(di, "good-class: %s.%s ", map->mod_name, query_class);
 			*class_id = idx + map->base;
 			return map;
 		}
 	}
+	for_subvec(i, cli, di, users) {
+		idx = match_string(cli->map->class_names, cli->map->length, query_class);
+		if (idx >= 0) {
+			v2pr_di_info(di, "class-ref: %s -> %s.%s ",
+				    cli->mod_name, cli->map->mod_name, query_class);
+			*class_id = idx + cli->map->base + cli->offset;
+			return cli->map;
+		}
+	}
 	*class_id = -ENOENT;
 	return NULL;
 }
@@ -238,8 +260,7 @@ static bool ddebug_match_desc(const struct ddebug_query *query,
 	return true;
 }
 
-static int ddebug_change(const struct ddebug_query *query,
-			 struct flag_settings *modifiers)
+static int ddebug_change(const struct ddebug_query *query, struct flag_settings *modifiers)
 {
 	int i;
 	struct ddebug_table *dt;
@@ -260,7 +281,8 @@ static int ddebug_change(const struct ddebug_query *query,
 			continue;
 
 		if (query->class_string) {
-			map = ddebug_find_valid_class(dt, query->class_string, &valid_class);
+			map = ddebug_find_valid_class(&dt->info, query->class_string,
+						      &valid_class);
 			if (!map)
 				continue;
 		} else {
@@ -593,7 +615,7 @@ static int ddebug_exec_query(char *query_string, const char *modname)
 
 /* handle multiple queries in query string, continue on error, return
    last error or number of matching callsites.  Module name is either
-   in param (for boot arg) or perhaps in query string.
+   in the modname arg (for boot args) or perhaps in query string.
 */
 static int ddebug_exec_queries(char *query, const char *modname)
 {
@@ -772,6 +794,7 @@ int param_get_dyndbg_classes(char *buffer, const struct kernel_param *kp)
 	default:
 		return -1;
 	}
+	return 0;
 }
 EXPORT_SYMBOL(param_get_dyndbg_classes);
 
@@ -1084,15 +1107,28 @@ static bool ddebug_class_in_range(const int class_id, const struct ddebug_class_
 		class_id < map->base + map->length);
 }
 
+static bool ddebug_user_class_in_range(const int class_id, const struct ddebug_class_user *cli)
+{
+	if (!cli || !cli->map)
+		return false;
+	int base = cli->map->base + cli->offset;
+	return (class_id >= base && class_id < base + cli->map->length);
+}
+
 static const char *ddebug_class_name(struct _ddebug_info *di, struct _ddebug *dp)
 {
 	struct ddebug_class_map *map;
+	struct ddebug_class_user *cli;
 	int i;
 
 	for_subvec(i, map, di, maps)
 		if (ddebug_class_in_range(dp->class_id, map))
 			return map->class_names[dp->class_id - map->base];
 
+	for_subvec(i, cli, di, users)
+		if (ddebug_user_class_in_range(dp->class_id, cli))
+			return cli->map->class_names[dp->class_id - cli->map->base - cli->offset];
+
 	return NULL;
 }
 
@@ -1173,6 +1209,140 @@ static const struct proc_ops proc_fops = {
 	.proc_write = ddebug_proc_write
 };
 
+#define vpr_cm_info(cm_p, msg_fmt, ...) ({				\
+	struct ddebug_class_map const *_cm = cm_p;			\
+	v2pr_info(msg_fmt "%s [%d..%d] %s..%s\n", ##__VA_ARGS__,	\
+		  _cm->mod_name, _cm->base, _cm->base + _cm->length,	\
+		  _cm->class_names[0], _cm->class_names[_cm->length - 1]); \
+	})
+
+/*
+ * Modules which define classmaps get them initialized by
+ * param-callback via module.c:parse_one.  Modules which use other's
+ * classmaps must be initialized explicitly.
+ */
+static inline u32 ddebug_class_param_to_bits(const struct ddebug_class_param *dcp)
+{
+	const struct ddebug_class_map *map = dcp->map;
+
+	switch (map->map_type) {
+	case DD_CLASS_TYPE_DISJOINT_BITS:
+		return *dcp->bits & CLASSMAP_BITMASK(map->length);
+	case DD_CLASS_TYPE_LEVEL_NUM:
+		return CLASSMAP_BITMASK(min_t(u32, *dcp->lvl, map->length));
+	default:
+		return 0;
+	}
+}
+
+static void __maybe_unused ddebug_class_param_clamp_input(u32 *inrep, const struct kernel_param *kp)
+{
+	const struct ddebug_class_param *dcp = kp->arg;
+	const struct ddebug_class_map *map = dcp->map;
+
+	switch (map->map_type) {
+	case DD_CLASS_TYPE_DISJOINT_BITS:
+		/* expect bits. mask and warn if too many */
+		if (*inrep & ~CLASSMAP_BITMASK(map->length)) {
+			pr_warn("%s: input: 0x%x exceeds mask: 0x%x, masking\n",
+				KP_NAME(kp), *inrep, CLASSMAP_BITMASK(map->length));
+			*inrep &= CLASSMAP_BITMASK(map->length);
+		}
+		break;
+	case DD_CLASS_TYPE_LEVEL_NUM:
+		/* input is bitpos, of highest verbosity to be enabled */
+		if (*inrep > map->length) {
+			pr_warn("%s: level:%d exceeds max:%d, clamping\n",
+				KP_NAME(kp), *inrep, map->length);
+			*inrep = map->length;
+		}
+		break;
+	}
+}
+
+/* called for class-users only, parse_one does this for definer modules */
+static void ddebug_sync_classbits(const struct kernel_param *kp, const char *modname)
+{
+	const struct ddebug_class_param *dcp = kp->arg;
+	u32 val, new_bits, init_bits;
+
+	if (!dcp || !dcp->map)
+		return;
+
+	init_bits = (_DPRINTK_FLAGS_DEFAULT & _DPRINTK_FLAGS_PRINT) ?
+		CLASSMAP_BITMASK(dcp->map->length) : 0;
+
+	switch (dcp->map->map_type) {
+	case DD_CLASS_TYPE_DISJOINT_BITS:
+		val = READ_ONCE(*dcp->bits);
+		new_bits = val;
+		v2pr_info("  %s: classbits: 0x%x\n", KP_NAME(kp), new_bits);
+		ddebug_apply_class_bitmap(dcp, &new_bits, init_bits, modname);
+		break;
+	case DD_CLASS_TYPE_LEVEL_NUM:
+		val = READ_ONCE(*dcp->lvl);
+		new_bits = CLASSMAP_BITMASK(val);
+		v2pr_info("  %s: lvl:%d bits:0x%x\n", KP_NAME(kp), val, new_bits);
+		ddebug_apply_class_bitmap(dcp, &new_bits, init_bits, modname);
+		break;
+	default:
+		pr_err("bad map type %d\n", dcp->map->map_type);
+		return;
+	}
+}
+
+static void ddebug_match_apply_kparam(const struct kernel_param *kp,
+				      const struct ddebug_class_map *map,
+				      const char *mod_name)
+{
+	struct ddebug_class_param *dcp;
+
+	if (kp->ops != &param_ops_dyndbg_classes)
+		return;
+
+	dcp = (struct ddebug_class_param *)kp->arg;
+
+	if (dcp && dcp->map == map) {
+		v2pr_info(" kp:%s.%s =0x%x", mod_name, kp->name, *dcp->bits);
+		vpr_cm_info(map, " %s maps ", mod_name);
+		ddebug_sync_classbits(kp, mod_name);
+	}
+}
+
+static void ddebug_apply_params(const struct ddebug_class_map *cm, const char *mod_name)
+{
+	const struct kernel_param *kp;
+
+	if (!cm)
+		return;
+#if IS_ENABLED(CONFIG_MODULES)
+	int i;
+
+	if (cm->mod) {
+		vpr_cm_info(cm, "loaded classmap: %s ", mod_name);
+		/* ifdef protects the cm->mod->kp deref */
+		for (i = 0, kp = cm->mod->kp; i < cm->mod->num_kp; i++, kp++)
+			ddebug_match_apply_kparam(kp, cm, mod_name);
+	}
+#endif
+	if (!cm->mod) {
+		vpr_cm_info(cm, "builtin classmap: %s ", mod_name);
+		for (kp = __start___param; kp < __stop___param; kp++)
+			ddebug_match_apply_kparam(kp, cm, mod_name);
+	}
+}
+
+static void ddebug_apply_class_users(const struct _ddebug_info *di)
+{
+	struct ddebug_class_user *cli;
+	int i;
+
+	for_subvec(i, cli, di, users)
+		ddebug_apply_params(cli->map, cli->mod_name);
+
+	v2pr_di_info(di, "attached %d class-users to ", i);
+}
+
 /*
  * dd_set_module_subrange - find matching subrange of classmaps
  * @_i:   caller-provided index var
@@ -1210,6 +1380,7 @@ static int ddebug_add_module(struct _ddebug_info *di)
 {
 	struct ddebug_table *dt;
 	struct ddebug_class_map *cm;
+	struct ddebug_class_user *cli;
 	int i;
 
 	if (!di->descs.len)
@@ -1222,6 +1393,7 @@ static int ddebug_add_module(struct _ddebug_info *di)
 		pr_err("error adding module: %s\n", di->mod_name);
 		return -ENOMEM;
 	}
+	INIT_LIST_HEAD(&dt->link);
 	/*
 	 * For built-in modules, di is a partial cursor into the
 	 * builtin dyndbg data; the descriptors are the subrange
@@ -1238,12 +1410,17 @@ static int ddebug_add_module(struct _ddebug_info *di)
 	 */
 	dt->info = *di;
 	dd_set_module_subrange(i, cm, &dt->info, maps);
+	dd_set_module_subrange(i, cli, &dt->info, users);
 
 	mutex_lock(&ddebug_lock);
 	list_add_tail(&dt->link, &ddebug_tables);
 	mutex_unlock(&ddebug_lock);
 
-	vpr_info("%3u debug prints in module %s\n", di->descs.len, di->mod_name);
+	if (dt->info.users.len)
+		ddebug_apply_class_users(&dt->info);
+
+	vpr_info("%3u debug prints in module %s\n",
+		 dt->info.descs.len, dt->info.mod_name);
 	return 0;
 }
 
@@ -1393,8 +1570,10 @@ static int __init dynamic_debug_init(void)
 	struct _ddebug_info di = {
 		.descs.start = __start___dyndbg_descs,
 		.maps.start  = __start___dyndbg_class_maps,
+		.users.start = __start___dyndbg_class_users,
 		.descs.len = __stop___dyndbg_descs - __start___dyndbg_descs,
 		.maps.len  = __stop___dyndbg_class_maps - __start___dyndbg_class_maps,
+		.users.len = __stop___dyndbg_class_users - __start___dyndbg_class_users,
 	};
 
 #ifdef CONFIG_MODULES
diff --git a/lib/test_dynamic_debug.c b/lib/test_dynamic_debug.c
index 9e8e028461ad..34e51996aa20 100644
--- a/lib/test_dynamic_debug.c
+++ b/lib/test_dynamic_debug.c
@@ -6,11 +6,30 @@
  *      Jim Cromie	<jim.cromie@gmail.com>
  */
 
-#define pr_fmt(fmt) "test_dd: " fmt
+/*
+ * This file is built 2x, also making test_dynamic_debug_submod.ko,
+ * whose 2-line src file #includes this file.  This gives us a _submod
+ * clone with identical pr_debugs, without further maintenance.
+ *
+ * If things are working properly, they should operate identically
+ * when printed or adjusted by >control.  This eases visual perusal of
+ * the logs, and simplifies testing, by easing the proper accounting
+ * of expectations.
+ *
+ * It also puts both halves of the subsystem _DEFINE & _USE use case
+ * together, and integrates the common ENUM providing both class_ids
+ * and class-names to both _DEFINErs and _USERs.  I think this makes
+ * the usage clearer.
+ */
+#if defined(TEST_DYNAMIC_DEBUG_SUBMOD)
+  #define pr_fmt(fmt) "test_dd_submod: " fmt
+#else
+  #define pr_fmt(fmt) "test_dd: " fmt
+#endif
 
 #include <linux/module.h>
 
-/* run tests by reading or writing sysfs node: do_prints */
+/* re-gen output by reading or writing sysfs node: do_prints */
 
 static void do_prints(void); /* device under test */
 static int param_set_do_prints(const char *instr, const struct kernel_param *kp)
@@ -39,14 +58,36 @@ module_param_cb(do_prints, &param_ops_do_prints, NULL, 0600);
  * Additionally, here:
  * - tie together sysname, mapname, bitsname, flagsname
  */
-#define DD_SYS_WRAP(_model, _flags)					\
-	static u32 bits_##_model;					\
-	static struct ddebug_class_param _flags##_model = {		\
+#define DYNAMIC_DEBUG_CLASSMAP_PARAM_(_model, _flags, _init)		\
+	static u32 bits_##_model = _init;				\
+	static struct ddebug_class_param _flags##_##_model = {		\
 		.bits = &bits_##_model,					\
 		.flags = #_flags,					\
 		.map = &map_##_model,					\
 	};								\
-	module_param_cb(_flags##_##_model, &param_ops_dyndbg_classes, &_flags##_model, 0600)
+	module_param_cb(_flags##_##_model, &param_ops_dyndbg_classes,	\
+			&_flags##_##_model, 0600)
+#ifdef DEBUG
+#define DYNAMIC_DEBUG_CLASSMAP_PARAM(_model, _flags)		\
+	DYNAMIC_DEBUG_CLASSMAP_PARAM_(_model, _flags, ~0)
+#else
+#define DYNAMIC_DEBUG_CLASSMAP_PARAM(_model, _flags)		\
+	DYNAMIC_DEBUG_CLASSMAP_PARAM_(_model, _flags, 0)
+#endif
+
+/*
+ * Demonstrate/test DISJOINT & LEVEL typed classmaps with a sys-param.
+ *
+ * To comport with DRM debug-category (an int), classmaps map names to
+ * ids (also an int).  So a classmap starts with an enum; DRM has enum
+ * debug_category: with DRM_UT_<CORE,DRIVER,KMS,etc>.  We use the enum
+ * values as class-ids, and stringified enum-symbols as classnames.
+ *
+ * Modules with multiple CLASSMAPS must have enums with distinct
+ * value-ranges, as arranged below with explicit enum_sym = X inits.
+ * To clarify this sharing, declare the 2 enums now, for the 2
+ * different classmap types
+ */
 
 /* numeric input, independent bits */
 enum cat_disjoint_bits {
@@ -60,26 +101,53 @@ enum cat_disjoint_bits {
 	D2_LEASE,
 	D2_DP,
 	D2_DRMRES };
-DECLARE_DYNDBG_CLASSMAP(map_disjoint_bits, DD_CLASS_TYPE_DISJOINT_BITS, 0,
-			"D2_CORE",
-			"D2_DRIVER",
-			"D2_KMS",
-			"D2_PRIME",
-			"D2_ATOMIC",
-			"D2_VBL",
-			"D2_STATE",
-			"D2_LEASE",
-			"D2_DP",
-			"D2_DRMRES");
-DD_SYS_WRAP(disjoint_bits, p);
-DD_SYS_WRAP(disjoint_bits, T);
-
-/* numeric verbosity, V2 > V1 related */
-enum cat_level_num { V0 = 14, V1, V2, V3, V4, V5, V6, V7 };
-DECLARE_DYNDBG_CLASSMAP(map_level_num, DD_CLASS_TYPE_LEVEL_NUM, 14,
-		       "V0", "V1", "V2", "V3", "V4", "V5", "V6", "V7");
-DD_SYS_WRAP(level_num, p);
-DD_SYS_WRAP(level_num, T);
+
+/* numeric verbosity, V2 > V1 related.  V1 is > D2_DRMRES */
+enum cat_level_num { V1 = 16, V2, V3, V4, V5, V6, V7 };
+
+/* recapitulate DRM's multi-classmap setup */
+#if !defined(TEST_DYNAMIC_DEBUG_SUBMOD)
+/*
+ * In single user, or parent / coordinator (drm.ko) modules, define
+ * classmaps on the client enums above, and then declares the PARAMS
+ * ref'g the classmaps.  Each is exported.
+ */
+DYNAMIC_DEBUG_CLASSMAP_DEFINE(map_disjoint_bits, DD_CLASS_TYPE_DISJOINT_BITS,
+			      D2_CORE,
+			      "D2_CORE",
+			      "D2_DRIVER",
+			      "D2_KMS",
+			      "D2_PRIME",
+			      "D2_ATOMIC",
+			      "D2_VBL",
+			      "D2_STATE",
+			      "D2_LEASE",
+			      "D2_DP",
+			      "D2_DRMRES");
+
+DYNAMIC_DEBUG_CLASSMAP_DEFINE(map_level_num, DD_CLASS_TYPE_LEVEL_NUM,
+			      V1, "V1", "V2", "V3", "V4", "V5", "V6", "V7");
+
+#else /* TEST_DYNAMIC_DEBUG_SUBMOD */
+
+/*
+ * in submod/drm-drivers, use the classmaps defined in top/parent
+ * module above.
+ */
+
+DYNAMIC_DEBUG_CLASSMAP_USE(map_disjoint_bits);
+DYNAMIC_DEBUG_CLASSMAP_USE_(map_level_num, 7);
+
+enum cat_level_offset { Vu1 = V1 + 7, Vu2, Vu3, Vu4, Vu5, Vu6, Vu7 };
+
+#endif
+
+/*
+ * now add the sysfs-params
+ */
+
+DYNAMIC_DEBUG_CLASSMAP_PARAM(disjoint_bits, p);
+DYNAMIC_DEBUG_CLASSMAP_PARAM(level_num, p);
 
 /* stand-in for all pr_debug etc */
 #define prdbg(SYM) __pr_debug_cls(SYM, #SYM " msg\n")
@@ -104,6 +172,7 @@ static void do_levels(void)
 {
 	pr_debug("doing levels\n");
 
+#if !defined(TEST_DYNAMIC_DEBUG_SUBMOD)
 	prdbg(V1);
 	prdbg(V2);
 	prdbg(V3);
@@ -111,10 +180,20 @@ static void do_levels(void)
 	prdbg(V5);
 	prdbg(V6);
 	prdbg(V7);
+#else
+	prdbg(Vu1);
+	prdbg(Vu2);
+	prdbg(Vu3);
+	prdbg(Vu4);
+	prdbg(Vu5);
+	prdbg(Vu6);
+	prdbg(Vu7);
+#endif
 }
 
 static void do_prints(void)
 {
+	pr_debug("do_prints:\n");
 	do_cats();
 	do_levels();
 }
diff --git a/lib/test_dynamic_debug_submod.c b/lib/test_dynamic_debug_submod.c
new file mode 100644
index 000000000000..672aabf40160
--- /dev/null
+++ b/lib/test_dynamic_debug_submod.c
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Kernel module for testing dynamic_debug
+ *
+ * Authors:
+ *      Jim Cromie	<jim.cromie@gmail.com>
+ */
+
+/*
+ * clone the parent, inherit all the properties, for consistency and
+ * simpler accounting in test expectations.
+ */
+#define TEST_DYNAMIC_DEBUG_SUBMOD
+#include "test_dynamic_debug.c"

-- 
2.55.0