diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 659bf3b31c91..5beb0321613e 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -373,6 +373,7 @@
 	/* implement dynamic printk debug */				\
 	. = ALIGN(8);							\
 	BOUNDED_SECTION_BY(__dyndbg_classes, ___dyndbg_classes)		\
+	BOUNDED_SECTION_BY(__dyndbg_class_refs, ___dyndbg_class_refs)	\
 	BOUNDED_SECTION_BY(__dyndbg, ___dyndbg)				\
 	LIKELY_PROFILE()		       				\
 	BRANCH_PROFILE()						\
diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 1cdfd62fd2e4..397ac8294230 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -81,8 +81,8 @@ enum ddebug_class_map_type {
 };
 
 struct ddebug_class_map {
-	struct module *mod;
-	const char *mod_name;	/* needed for builtins */
+	const struct module *mod;		/* NULL for builtins */
+	const char *mod_name;
 	const char **class_names;
 	const int length;
 	const int base;		/* index of 1st .class_id, allows split/shared space */
@@ -99,8 +99,8 @@ struct ddebug_class_map {
  * @classes: class-names used to control class'd prdbgs
  */
 #define DYNDBG_CLASSMAP_DEFINE(_var, _maptype, _base, ...)		\
-	static const char *_var##_classnames[] = { __VA_ARGS__ };	\
-	static struct ddebug_class_map __aligned(8) __used		\
+	const char *_var##_classnames[] = { __VA_ARGS__ };		\
+	struct ddebug_class_map __aligned(8) __used			\
 		__section("__dyndbg_classes") _var = {			\
 		.mod = THIS_MODULE,					\
 		.mod_name = KBUILD_MODNAME,				\
@@ -108,24 +108,37 @@ struct ddebug_class_map {
 		.map_type = _maptype,					\
 		.length = ARRAY_SIZE(_var##_classnames),		\
 		.class_names = _var##_classnames,			\
-	}
+	};								\
+	EXPORT_SYMBOL(_var)
 
-/*
- * refer to the classmap instantiated once, by the macro above.  This
- * distinguishes the multiple users of drm.debug from the single
- * definition, allowing them to specialize.  ATM its a pass-thru, but
- * it should help regularize the admittedly wierd sharing by identical
- * definitions.
+struct ddebug_class_user {
+	char *user_mod_name;
+	struct ddebug_class_map *map;
+};
+/**
+ * DYNDBG_CLASSMAP_USE - Use a classmap DEFINEd in another module.
+ * This lets dyndbg initialize the dependent module's prdbgs from the
+ * other module's controlling sysfs node.
  */
-#define DYNDBG_CLASSMAP_USE(_var, _maptype, _base, ...)		\
-	DYNDBG_CLASSMAP_DEFINE(_var, _maptype, _base, __VA_ARGS__)
+#define DYNDBG_CLASSMAP_USE(_var, ...)					\
+	DYNDBG_CLASSMAP_USE_(_var, __UNIQUE_ID(ddebug_class_user),	\
+			     __VA_ARGS__)
+#define DYNDBG_CLASSMAP_USE_(_var, _uname, ...)				\
+	extern struct ddebug_class_map _var;				\
+	static struct ddebug_class_user __used				\
+	__section("__dyndbg_class_refs") _uname = {			\
+		.user_mod_name = KBUILD_MODNAME,			\
+		.map = &_var,						\
+	}
 
 /* encapsulate linker provided built-in (or module) dyndbg data */
 struct _ddebug_info {
 	struct _ddebug *descs;
 	struct ddebug_class_map *classes;
+	struct ddebug_class_user *class_refs;
 	unsigned int num_descs;
 	unsigned int num_classes;
+	unsigned int num_class_refs;
 };
 
 struct ddebug_class_param {
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 48568a0f5651..cfccbd06ae2d 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2113,6 +2113,9 @@ static int find_module_sections(struct module *mod, struct load_info *info)
 					sizeof(*info->dyndbg.descs), &info->dyndbg.num_descs);
 	info->dyndbg.classes = section_objs(info, "__dyndbg_classes",
 					sizeof(*info->dyndbg.classes), &info->dyndbg.num_classes);
+	info->dyndbg.class_refs = section_objs(info, "__dyndbg_class_refs",
+					       sizeof(*info->dyndbg.class_refs),
+					       &info->dyndbg.num_class_refs);
 
 	return 0;
 }
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index b51f4bde6198..57efd435dda7 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -43,13 +43,16 @@ extern struct _ddebug __start___dyndbg[];
 extern struct _ddebug __stop___dyndbg[];
 extern struct ddebug_class_map __start___dyndbg_classes[];
 extern struct ddebug_class_map __stop___dyndbg_classes[];
+extern struct ddebug_class_user __start___dyndbg_class_refs[];
+extern struct ddebug_class_user __stop___dyndbg_class_refs[];
 
 struct ddebug_table {
 	struct list_head link;
 	const char *mod_name;
 	struct _ddebug *ddebugs;
 	struct ddebug_class_map *classes;
-	unsigned int num_ddebugs, num_classes;
+	struct ddebug_class_user *class_refs;
+	unsigned int num_ddebugs, num_classes, num_class_refs;
 };
 
 struct ddebug_query {
@@ -147,21 +150,36 @@ static void vpr_info_dq(const struct ddebug_query *query, const char *msg)
 		  query->first_lineno, query->last_lineno, query->class_string);
 }
 
+#define vpr_dt_info(dt, _msg, ...)					\
+	v2pr_info(_msg " module:%s nd:%d nc:%d nu:%d\n", ##__VA_ARGS__,	\
+		  dt->mod_name, dt->num_ddebugs, dt->num_classes, dt->num_class_refs)
+
 #define __outvar /* filled by callee */
 static struct ddebug_class_map *ddebug_find_valid_class(struct ddebug_table const *dt,
 							const char *class_string,
 							__outvar int *class_id)
 {
 	struct ddebug_class_map *map;
+	struct ddebug_class_user *cli;
 	int i, idx;
 
-	for (map = dt->classes, i = 0; i < dt->num_classes; i++, map++) {
+	for (i = 0, map = dt->classes; i < dt->num_classes; i++, map++) {
 		idx = match_string(map->class_names, map->length, class_string);
 		if (idx >= 0) {
 			*class_id = idx + map->base;
+			vpr_dt_info(dt, "good-class: %s.%s ", map->mod_name, class_string);
 			return map;
 		}
 	}
+	for (i = 0, cli = dt->class_refs; i < dt->num_class_refs; i++, cli++) {
+		idx = match_string(cli->map->class_names, cli->map->length, class_string);
+		if (idx >= 0) {
+			*class_id = idx + cli->map->base;
+			vpr_dt_info(dt, "class-ref: %s.%s ",
+				    cli->user_mod_name, class_string);
+			return cli->map;
+		}
+	}
 	*class_id = -ENOENT;
 	return NULL;
 }
@@ -590,9 +608,10 @@ static int ddebug_exec_queries(char *query, const char *modname)
 	return nfound;
 }
 
-/* apply a new bitmap to the sys-knob's current bit-state */
+/* apply a new class-param setting */
 static int ddebug_apply_class_bitmap(const struct ddebug_class_param *dcp,
-				     const unsigned long *new_bits, const unsigned long *old_bits,
+				     const unsigned long *new_bits,
+				     const unsigned long *old_bits,
 				     const char *query_modname)
 {
 #define QUERY_SIZE 128
@@ -601,8 +620,9 @@ static int ddebug_apply_class_bitmap(const struct ddebug_class_param *dcp,
 	int matches = 0;
 	int bi, ct;
 
-	v2pr_info("apply bitmap: 0x%lx to: 0x%lx for %s\n", *new_bits, *old_bits,
-		  query_modname ?: "");
+	if (*new_bits != *old_bits)
+		v2pr_info("apply bitmap: 0x%lx to: 0x%lx for %s\n", *new_bits,
+			  *old_bits, query_modname ?: "'*'");
 
 	for (bi = 0; bi < map->length; bi++) {
 		if (test_bit(bi, new_bits) == test_bit(bi, old_bits))
@@ -617,8 +637,9 @@ static int ddebug_apply_class_bitmap(const struct ddebug_class_param *dcp,
 		v2pr_info("bit_%d: %d matches on class: %s -> 0x%lx\n", bi,
 			  ct, map->class_names[bi], *new_bits);
 	}
-	v2pr_info("applied bitmap: 0x%lx to: 0x%lx for %s\n", *new_bits, *old_bits,
-		  query_modname ?: "");
+	if (*new_bits != *old_bits)
+		v2pr_info("applied bitmap: 0x%lx to: 0x%lx for %s\n", *new_bits,
+			  *old_bits, query_modname ?: "'*'");
 
 	return matches;
 }
@@ -707,6 +728,7 @@ static int param_set_dyndbg_module_classes(const char *instr,
 	const struct ddebug_class_map *map = dcp->map;
 	unsigned long inrep, new_bits, old_bits;
 	int rc, totct = 0;
+	char *nl;
 
 	switch (map->map_type) {
 
@@ -720,7 +742,10 @@ static int param_set_dyndbg_module_classes(const char *instr,
 		/* numeric input, accept and fall-thru */
 		rc = kstrtoul(instr, 0, &inrep);
 		if (rc) {
-			pr_err("expecting numeric input: %s > %s\n", instr, KP_NAME(kp));
+			nl = strchr(instr, '\n');
+			if (nl)
+				*nl = '\0';
+			pr_err("expecting numeric input, not: %s > %s\n", instr, KP_NAME(kp));
 			return -EINVAL;
 		}
 		break;
@@ -1113,12 +1138,17 @@ static void *ddebug_proc_next(struct seq_file *m, void *p, loff_t *pos)
 static const char *ddebug_class_name(struct ddebug_table *dt, struct _ddebug *dp)
 {
 	struct ddebug_class_map *map = dt->classes;
+	struct ddebug_class_user *cli = dt->class_refs;
 	int i;
 
 	for (i = 0; i < dt->num_classes; i++, map++)
 		if (class_in_range(dp->class_id, map))
 			return map->class_names[dp->class_id - map->base];
 
+	for (i = 0; i < dt->num_class_refs; i++, cli++)
+		if (class_in_range(dp->class_id, cli->map))
+			return cli->map->class_names[dp->class_id - cli->map->base];
+
 	return NULL;
 }
 
@@ -1199,33 +1229,125 @@ static const struct proc_ops proc_fops = {
 	.proc_write = ddebug_proc_write
 };
 
+
+/*
+ * Find this module's classmaps in a sub/whole-range of the builtin/
+ * modular classmap vector/section.  Save the start and length of the
+ * subrange at its edges.
+ */
 static void ddebug_attach_module_classes(struct ddebug_table *dt, struct _ddebug_info *di)
 {
 	struct ddebug_class_map *cm;
 	int i, nc = 0;
 
-	/*
-	 * Find this module's classmaps in a subrange/wholerange of
-	 * the builtin/modular classmap vector/section.  Save the start
-	 * and length of the subrange at its edges.
-	 */
-	for (cm = di->classes, i = 0; i < di->num_classes; i++, cm++) {
+	for (i = 0, cm = di->classes; i < di->num_classes; i++, cm++) {
 
 		if (!strcmp(cm->mod_name, dt->mod_name)) {
 			if (!nc) {
-				v2pr_info("start subrange, class[%d]: module:%s base:%d len:%d ty:%d\n",
-					  i, cm->mod_name, cm->base, cm->length, cm->map_type);
 				dt->classes = cm;
+				v2pr_info("classes[0..]: module:%s base:%d len:%d ty:%d\n",
+					  cm->mod_name, cm->base, cm->length, cm->map_type);
 			}
 			nc++;
 		}
 	}
-	if (nc) {
-		dt->num_classes = nc;
+	dt->num_classes = nc;
+	if (nc)
 		vpr_info("module:%s attached %d classes\n", dt->mod_name, nc);
+}
+
+#define vpr_cm_info(cm, _msg, ...)					\
+	v2pr_info(_msg " module:%s base:%d len:%d type:%d\n", ##__VA_ARGS__, \
+		  cm->mod_name, cm->base, cm->length, cm->map_type)
+
+static void ddebug_match_apply_kparam(const struct kernel_param *kp, struct ddebug_class_user *cli)
+{
+	struct ddebug_class_param *dcp;
+	unsigned long new_bits, old_bits = 0;
+	int totct = 0;
+
+	if (kp->ops != &param_ops_dyndbg_classes)
+		return;
+
+	dcp = (struct ddebug_class_param *)kp->arg;
+
+	if (cli->map == dcp->map) {
+		v2pr_info("found kp:%s =0x%lx", kp->name, *dcp->bits);
+		vpr_cm_info(cli->map, "mapped to:");
+		/*
+		 * using apply-bitmap is too low.
+		 * param_set_dyndbg_classes uses map_type to sort
+		 * levels-to-bits.
+		 * param_set_dyndbg_classes is too high, it takes
+		 * string inputs.
+		 * de-union-ing levels/bits might solve it (partly),
+		 * at least simplifying the translation, and possibly
+		 * the apply-bitmap fn/iface
+		 */
+		new_bits = *dcp->bits;
+		totct += ddebug_apply_class_bitmap(dcp, &new_bits, &old_bits,
+						   cli->user_mod_name);
+	}
+}
+
+static void ddebug_apply_parents_params(struct ddebug_class_user *cli)
+{
+	const struct ddebug_class_map *cm = cli->map;
+	const struct kernel_param *kp;
+#if IS_ENABLED(CONFIG_MODULES)
+	int i;
+
+	if (cm->mod) {
+		vpr_cm_info(cm, "loaded class:");
+		for (i = 0, kp = cm->mod->kp; i < cm->mod->num_kp; i++, kp++)
+			ddebug_match_apply_kparam(kp, cli);
+	}
+#endif
+	if (!cm->mod) {
+		vpr_cm_info(cm, "builtin class:");
+		for (kp = __start___param; kp < __stop___param; kp++)
+			ddebug_match_apply_kparam(kp, cli);
 	}
 }
 
+/*
+ * propagates class-params thru their classmaps to class-users.  this
+ * means a query against the dt/module, which means it must be on the
+ * list to be seen by ddebug_change.
+ */
+static void ddebug_attach_client_module_classes(struct ddebug_table *dt, const struct _ddebug_info *di)
+{
+	struct ddebug_class_user *cli;
+	int i, nc = 0;
+
+	/*
+	 * For builtins: scan the array, find start/length of this
+	 * module's refs, save to dt.  For loadables, this is the
+	 * whole array.
+	 */
+	for (i = 0, cli = di->class_refs; i < di->num_class_refs; i++, cli++) {
+
+		if (WARN_ON(!cli || !cli->map || !cli->user_mod_name))
+			continue;
+
+		if (!strcmp(cli->user_mod_name, dt->mod_name)) {
+
+			v2pr_info("class_ref[%d] %s -> %s\n", i,
+				  cli->user_mod_name, cli->map->mod_name);
+
+			if (!nc++)
+				dt->class_refs = cli;
+		}
+	}
+	dt->num_class_refs = nc;
+
+	/* now iterate dt */
+	for (i = 0, cli = dt->class_refs; i < dt->num_class_refs; i++, cli++)
+		ddebug_apply_parents_params(cli);
+
+	vpr_dt_info(dt, "attach-client-module: ");
+}
+
 /*
  * Allocate a new ddebug_table for the given module
  * and add it to the global list.
@@ -1235,7 +1357,8 @@ static int __ddebug_add_module(struct _ddebug_info *di, unsigned int base,
 {
 	struct ddebug_table *dt;
 
-	v3pr_info("add-module: %s.%d sites\n", modname, di->num_descs);
+	v3pr_info("add-module: %s %d sites %d.%d\n", modname, di->num_descs,
+		  di->num_classes, di->num_class_refs);
 	if (!di->num_descs) {
 		v3pr_info(" skip %s\n", modname);
 		return 0;
@@ -1258,13 +1381,16 @@ static int __ddebug_add_module(struct _ddebug_info *di, unsigned int base,
 
 	INIT_LIST_HEAD(&dt->link);
 
-	if (di->classes && di->num_classes)
+	if (di->num_classes)
 		ddebug_attach_module_classes(dt, di);
 
 	mutex_lock(&ddebug_lock);
 	list_add_tail(&dt->link, &ddebug_tables);
 	mutex_unlock(&ddebug_lock);
 
+	if (di->num_class_refs)
+		ddebug_attach_client_module_classes(dt, di);
+
 	vpr_info("%3u debug prints in module %s\n", di->num_descs, modname);
 	return 0;
 }
@@ -1390,8 +1516,10 @@ static int __init dynamic_debug_init(void)
 	struct _ddebug_info di = {
 		.descs = __start___dyndbg,
 		.classes = __start___dyndbg_classes,
+		.class_refs = __start___dyndbg_class_refs,
 		.num_descs = __stop___dyndbg - __start___dyndbg,
 		.num_classes = __stop___dyndbg_classes - __start___dyndbg_classes,
+		.num_class_refs = __stop___dyndbg_class_refs - __start___dyndbg_class_refs,
 	};
 
 	if (&__start___dyndbg == &__stop___dyndbg) {
