regmap: Disable debugfs when locking is disabled

The recently added support for disabling the regmap internal locking left
debugfs enabled for devices with the locking disabled. This is a problem
since debugfs allows userspace to do things like initiate reads from the
hardware which will use the scratch buffers protected by the regmap locking
so could cause data corruption.

For safety address this by just disabling debugfs for these devices. That
is overly conservative since some of the debugfs files just read internal
data structures but it's much simpler to implmement and less likely to
lead to problems with tooling that works with debugfs.

Reported-by: Lars-Peter Clausen <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/base/regmap/internal.h

···
 	int async_ret;
 
 #ifdef CONFIG_DEBUG_FS
+	bool debugfs_disable;
 	struct dentry *debugfs;
 	const char *debugfs_name;
 
···
 extern void regmap_debugfs_initcall(void);
 extern void regmap_debugfs_init(struct regmap *map, const char *name);
 extern void regmap_debugfs_exit(struct regmap *map);
+
+static inline void regmap_debugfs_disable(struct regmap *map)
+{
+	map->debugfs_disable = true;
+}
+
 #else
 static inline void regmap_debugfs_initcall(void) { }
 static inline void regmap_debugfs_init(struct regmap *map, const char *name) { }
 static inline void regmap_debugfs_exit(struct regmap *map) { }
+static inline void regmap_debugfs_disable(struct regmap *map) { }
 #endif
 
 /* regcache core declarations */

drivers/base/regmap/regmap-debugfs.c

···
 	struct regmap_range_node *range_node;
 	const char *devname = "dummy";
 
+	if (map->debugfs_disable)
+		return;
+
 	/* If we don't have the debugfs root yet, postpone init */
 	if (!regmap_debugfs_root) {
 		struct regmap_debugfs_node *node;

drivers/base/regmap/regmap.c

···
 
 	if (config->disable_locking) {
 		map->lock = map->unlock = regmap_lock_unlock_none;
+		regmap_debugfs_disable(map);
 	} else if (config->lock && config->unlock) {
 		map->lock = config->lock;
 		map->unlock = config->unlock;