diff --git a/lib/Makefile b/lib/Makefile
index 4d9461bfea42..7f7e75f44cd7 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -77,7 +77,7 @@ obj-$(CONFIG_TEST_SORT) += test_sort.o
 obj-$(CONFIG_TEST_USER_COPY) += test_user_copy.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) += test_dynamic_debug.o test_dynamic_debug_submod.o
 obj-$(CONFIG_TEST_PRINTF) += test_printf.o
 obj-$(CONFIG_TEST_SCANF) += test_scanf.o
 obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o
@@ -98,6 +98,7 @@ obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
 obj-$(CONFIG_TEST_REF_TRACKER) += test_ref_tracker.o
 CFLAGS_test_fprobe.o += $(CC_FLAGS_FTRACE)
 obj-$(CONFIG_FPROBE_SANITY_TEST) += test_fprobe.o
+
 #
 # CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns
 # off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS
diff --git a/lib/test_dynamic_debug.c b/lib/test_dynamic_debug.c
index e678884066bf..8c005c17f2db 100644
--- a/lib/test_dynamic_debug.c
+++ b/lib/test_dynamic_debug.c
@@ -6,7 +6,11 @@
  *      Jim Cromie	<jim.cromie@gmail.com>
  */
 
-#define pr_fmt(fmt) "test_dd: " fmt
+#if defined(TEST_DYNAMIC_DEBUG_SUBMOD)
+  #define pr_fmt(fmt) "test_dd_submod: " fmt
+#else
+  #define pr_fmt(fmt) "test_dd: " fmt
+#endif
 
 #define DEBUG /* enable all prdbgs (plain & class'd) at compiletime */
 
@@ -49,6 +53,14 @@ module_param_cb(do_prints, &param_ops_do_prints, NULL, 0600);
 	};								\
 	module_param_cb(_flags##_##_model, &param_ops_dyndbg_classes, &_flags##_model, 0600)
 
+/*
+ * dynamic-debug imitates drm.debug's use of enums (DRM_UT_CORE etc)
+ * to define its classes/categories.  dyndbg allows class-id's 0..62,
+ * reserving 63 for plain old (non-class'd) prdbgs.  A module can
+ * define multiple classmaps, as long as they claim non-overlapping
+ * subranges.
+ */
+
 /* numeric input, independent bits */
 enum cat_disjoint_bits {
 	D2_CORE = 0,
@@ -61,7 +73,36 @@ enum cat_disjoint_bits {
 	D2_LEASE,
 	D2_DP,
 	D2_DRMRES };
+
+/* symbolic input, independent bits */
+enum cat_disjoint_names { LOW = 10, MID, HI };
+
+/* numeric verbosity, V2 > V1 related */
+enum cat_level_num { V0 = 14, V1, V2, V3, V4, V5, V6, V7 };
+
+/* symbolic verbosity */
+enum cat_level_names { L0 = 22, L1, L2, L3, L4, L5, L6, L7 };
+
+#if defined(TEST_DYNAMIC_DEBUG_SUBMOD)
+
+/* use the classmaps defined in 'parent' module below */
+DYNDBG_CLASSMAP_USE(map_disjoint_bits);
+DYNDBG_CLASSMAP_USE(map_disjoint_names);
+DYNDBG_CLASSMAP_USE(map_level_num);
+DYNDBG_CLASSMAP_USE(map_level_names);
+
+#else
+
+/*
+ * parent module, define a classmap of each of 4 types.
+ * enum values are class-ids
+ * enum symbols are stringified, used as classnames
+ * param bits are mapped in order: 0..N
+ * (a straight, obvious, linear map is encouraged)
+ */
+
 DYNDBG_CLASSMAP_DEFINE(map_disjoint_bits, DD_CLASS_TYPE_DISJOINT_BITS,
+		       /* bits 0..N of param are mapped to these class-ids */
 		       D2_CORE,
 		       D2_DRIVER,
 		       D2_KMS,
@@ -75,27 +116,23 @@ DYNDBG_CLASSMAP_DEFINE(map_disjoint_bits, DD_CLASS_TYPE_DISJOINT_BITS,
 DD_SYS_WRAP(disjoint_bits, p);
 DD_SYS_WRAP(disjoint_bits, T);
 
-/* symbolic input, independent bits */
-enum cat_disjoint_names { LOW = 10, MID, HI };
 DYNDBG_CLASSMAP_DEFINE(map_disjoint_names, DD_CLASS_TYPE_DISJOINT_NAMES,
 		       LOW, MID, HI);
 DD_SYS_WRAP(disjoint_names, p);
 DD_SYS_WRAP(disjoint_names, T);
 
-/* numeric verbosity, V2 > V1 related */
-enum cat_level_num { V0 = 14, V1, V2, V3, V4, V5, V6, V7 };
 DYNDBG_CLASSMAP_DEFINE(map_level_num, DD_CLASS_TYPE_LEVEL_NUM,
 		       V0, V1, V2, V3, V4, V5, V6, V7);
 DD_SYS_WRAP(level_num, p);
 DD_SYS_WRAP(level_num, T);
 
-/* symbolic verbosity */
-enum cat_level_names { L0 = 22, L1, L2, L3, L4, L5, L6, L7 };
 DYNDBG_CLASSMAP_DEFINE(map_level_names, DD_CLASS_TYPE_LEVEL_NAMES,
 		       L0, L1, L2, L3, L4, L5, L6, L7);
 DD_SYS_WRAP(level_names, p);
 DD_SYS_WRAP(level_names, T);
 
+#endif /* TEST_DYNAMIC_DEBUG_SUBMOD */
+
 /* stand-in for all pr_debug etc */
 #define prdbg(SYM) __pr_debug_cls(SYM, #SYM " msg\n")
 
@@ -142,6 +179,7 @@ static void do_levels(void)
 
 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..9a893402ce1a
--- /dev/null
+++ b/lib/test_dynamic_debug_submod.c
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Kernel module for testing dynamic_debug
+ *
+ * Authors:
+ *      Jim Cromie	<jim.cromie@gmail.com>
+ */
+
+#define TEST_DYNAMIC_DEBUG_SUBMOD
+#include "test_dynamic_debug.c"
