drm: Add DRM-managed mutex_init()

Add drmm_mutex_init(), a helper that provides managed mutex cleanup. The
mutex will be destroyed with the final reference of the DRM device.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220502142514.2174-2-tzimmermann@suse.de

drivers/gpu/drm/drm_managed.c

@@ -8,6 +8,7 @@
 #include <drm/drm_managed.h>
 
 #include <linux/list.h>
+#include <linux/mutex.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 
@@ -262,3 +263,29 @@ void drmm_kfree(struct drm_device *dev, void *data)
 	free_dr(dr_match);
 }
 EXPORT_SYMBOL(drmm_kfree);
+
+static void drmm_mutex_release(struct drm_device *dev, void *res)
+{
+	struct mutex *lock = res;
+
+	mutex_destroy(lock);
+}
+
+/**
+ * drmm_mutex_init - &drm_device-managed mutex_init()
+ * @dev: DRM device
+ * @lock: lock to be initialized
+ *
+ * Returns:
+ * 0 on success, or a negative errno code otherwise.
+ *
+ * This is a &drm_device-managed version of mutex_init(). The initialized
+ * lock is automatically destroyed on the final drm_dev_put().
+ */
+int drmm_mutex_init(struct drm_device *dev, struct mutex *lock)
+{
+	mutex_init(lock);
+
+	return drmm_add_action_or_reset(dev, drmm_mutex_release, lock);
+}
+EXPORT_SYMBOL(drmm_mutex_init);

include/drm/drm_managed.h

@@ -8,6 +8,7 @@
 #include <linux/types.h>
 
 struct drm_device;
+struct mutex;
 
 typedef void (*drmres_release_t)(struct drm_device *dev, void *res);
 
@@ -104,4 +105,6 @@ char *drmm_kstrdup(struct drm_device *dev, const char *s, gfp_t gfp);
 
 void drmm_kfree(struct drm_device *dev, void *data);
 
+int drmm_mutex_init(struct drm_device *dev, struct mutex *lock);
+
 #endif