Message-ID: <20260129072932.2190803-32-jim.cromie@gmail.com>
Date: Thu, 29 Jan 2026 00:29:17 -0700
From: Jim Cromie <jim.cromie@...il.com>
To: gregkh@...uxfoundation.org
Cc: Jim Cromie <jim.cromie@...il.com>,
	Jason Baron <jbaron@...mai.com>,
	Łukasz Bartosik <ukaszb@...omium.org>,
	Louis Chauvet <louis.chauvet@...tlin.com>,
	Bagas Sanjaya <bagasdotme@...il.com>,
	Dave Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	dri-devel@...ts.freedesktop.org,
	Petr Mladek <pmladek@...e.com>,
	Shuah Khan <skhan@...uxfoundation.org>,
	linux-doc@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v9 31/32] dyndbg: add DYNAMIC_DEBUG_CLASSMAP_USE_(dd_class_name, offset)

Allow a module to use 2 classmaps together that would otherwise have a
class_id range conflict.

Suppose a drm-driver does:

  DYNAMIC_DEBUG_CLASSMAP_USE(drm_debug_classes);
  DYNAMIC_DEBUG_CLASSMAP_USE(drm_accel_xfer_debug);

If (for some reason) drm-accel cannot define their constants to avoid
DRM's drm_debug_category 0..10 reservations, we would have a conflict
with reserved-ids.

In this case a driver needing to use both would _USE_ one of them with
an offset to avoid the conflict.  This will handle most forseeable
cases; perhaps a 3-X-3 of classmap-defns X classmap-users would get
too awkward and fiddly.

This is an untested interface extension, so drop this patch if it
feels too speculative, knowing theres at least a notional solution
should the situation arise.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 include/linux/dynamic_debug.h | 27 ++++++++++++++++++++++-----
 lib/dynamic_debug.c           | 19 ++++++++++++-------
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index a1454db1bcb0..0d1245aefc69 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -88,7 +88,7 @@ struct _ddebug_class_map {
 struct _ddebug_class_user {
 	char *mod_name;
 	struct _ddebug_class_map *map;
-	const int offset;	/* user offset to re-number the used map */
+	const int offset;	/* offset from map->base */
 };
 
 /*
@@ -239,11 +239,28 @@ struct _ddebug_class_param {
  *
  * 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.
+ * 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, __UNIQUE_ID(_ddebug_class_user))
-#define DYNAMIC_DEBUG_CLASSMAP_USE_(_var, _offset, _uname)		\
+#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)			\
+	__DYNAMIC_DEBUG_CLASSMAP_USE(_var, _offset, __UNIQUE_ID(_ddebug_class_user))
+
+#define __DYNAMIC_DEBUG_CLASSMAP_USE(_var, _offset, _uname)		\
 	extern struct _ddebug_class_map _var;				\
 	static struct _ddebug_class_user __aligned(8) __used		\
 	__section("__dyndbg_class_users") _uname = {			\
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 4d42e857cc75..5568db8451af 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -199,7 +199,7 @@ ddebug_find_valid_class(struct _ddebug_info const *di, const char *query_class,
 		if (idx >= 0) {
 			vpr_di_info(di, "class-ref: %s -> %s.%s ",
 				    cli->mod_name, cli->map->mod_name, query_class);
-			*class_id = idx + cli->map->base;
+			*class_id = idx + cli->map->base - cli->offset;
 			return cli->map;
 		}
 	}
@@ -207,12 +207,17 @@ ddebug_find_valid_class(struct _ddebug_info const *di, const char *query_class,
 	return NULL;
 }
 
-static bool ddebug_class_in_range(const int class_id, const struct _ddebug_class_map *map)
+static bool ddebug_class_map_in_range(const int class_id, const struct _ddebug_class_map *map)
 {
 	return (class_id >= map->base &&
 		class_id < map->base + map->length);
 }
 
+static bool ddebug_class_user_in_range(const int class_id, const struct _ddebug_class_user *user)
+{
+	return ddebug_class_map_in_range(class_id - user->offset, user->map);
+}
+
 static struct _ddebug_class_map *
 ddebug_find_map_by_class_id(struct _ddebug_info *di, int class_id)
 {
@@ -221,11 +226,11 @@ ddebug_find_map_by_class_id(struct _ddebug_info *di, int class_id)
 	int i;
 
 	for_subvec(i, map, di, maps)
-		if (ddebug_class_in_range(class_id, map))
+		if (ddebug_class_map_in_range(class_id, map))
 			return map;
 
 	for_subvec(i, cli, di, users)
-		if (ddebug_class_in_range(class_id, cli->map))
+		if (ddebug_class_user_in_range(class_id, cli))
 			return cli->map;
 
 	return NULL;
@@ -1178,12 +1183,12 @@ static const char *ddebug_class_name(struct _ddebug_info *di, struct _ddebug *dp
 	int i;
 
 	for_subvec(i, map, di, maps)
-		if (ddebug_class_in_range(dp->class_id, map))
+		if (ddebug_class_map_in_range(dp->class_id, map))
 			return map->class_names[dp->class_id - map->base];
 
 	for_subvec(i, cli, di, users)
-		if (ddebug_class_in_range(dp->class_id, cli->map))
-			return cli->map->class_names[dp->class_id - cli->map->base];
+		if (ddebug_class_user_in_range(dp->class_id, cli))
+			return cli->map->class_names[dp->class_id - cli->map->base - cli->offset];
 
 	return NULL;
 }
-- 
2.52.0

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