drm: cleanup drm_core_{init,exit}()

Various cleanups to the DRM core initialization and exit handlers:

 - Register chrdev last: Once register_chrdev() returns, open() will
   succeed on the given chrdevs. This is usually not an issue, as no
   chardevs are registered, yet. However, nodes can be created by
   user-space via mknod(2), even though such major/minor combinations are
   unknown to the kernel. Avoid calling into drm_stub_open() in those
   cases.
   Again, drm_stub_open() would just bail out as the inode is unknown,
   but it's really non-obvious if you hack on drm_stub_open().

 - Unify error-paths into just one label. All the error-path helpers can
   be called even though the constructors were not called yet, or failed.
   Hence, just call all cleanups unconditionally.

 - Call into drm_global_release(). This is a no-op, but provides
   debugging helpers in case there're GLOBALS left on module unload. This
   function was unused until now.

 - Use DRM_ERROR() instead of printk(), and also print the error-code on
   failure (even if it is static!).

 - Don't throw away error-codes of register_chrdev()!

 - Don't hardcode -1 as errno. This is just plain wrong.

 - Order exit-handlers in the exact reverse order of initialization
   (except if the order actually matters for syncing-reasons, which is
   not the case here, though).

v2:
 - Call drm_core_exit() directly from the init-error-handler. Requires to
   drop __exit annotation, though.
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20160901124837.680-7-dh.herrmann@gmail.com

drivers/gpu/drm/drm_drv.c

@@ -820,52 +820,48 @@ static const struct file_operations drm_stub_fops = {
 	.llseek = noop_llseek,
 };
 
+static void drm_core_exit(void)
+{
+	unregister_chrdev(DRM_MAJOR, "drm");
+	debugfs_remove(drm_debugfs_root);
+	drm_sysfs_destroy();
+	idr_destroy(&drm_minors_idr);
+	drm_connector_ida_destroy();
+	drm_global_release();
+}
+
 static int __init drm_core_init(void)
 {
-	int ret = -ENOMEM;
+	int ret;
 
 	drm_global_init();
 	drm_connector_ida_init();
 	idr_init(&drm_minors_idr);
 
-	if (register_chrdev(DRM_MAJOR, "drm", &drm_stub_fops))
-		goto err_p1;
-
 	ret = drm_sysfs_init();
 	if (ret < 0) {
-		printk(KERN_ERR "DRM: Error creating drm class.\n");
-		goto err_p2;
+		DRM_ERROR("Cannot create DRM class: %d\n", ret);
+		goto error;
 	}
 
 	drm_debugfs_root = debugfs_create_dir("dri", NULL);
 	if (!drm_debugfs_root) {
-		DRM_ERROR("Cannot create /sys/kernel/debug/dri\n");
-		ret = -1;
-		goto err_p3;
+		ret = -ENOMEM;
+		DRM_ERROR("Cannot create debugfs-root: %d\n", ret);
+		goto error;
 	}
 
+	ret = register_chrdev(DRM_MAJOR, "drm", &drm_stub_fops);
+	if (ret < 0)
+		goto error;
+
 	DRM_INFO("Initialized\n");
 	return 0;
-err_p3:
-	drm_sysfs_destroy();
-err_p2:
-	unregister_chrdev(DRM_MAJOR, "drm");
 
-	idr_destroy(&drm_minors_idr);
-err_p1:
+error:
+	drm_core_exit();
 	return ret;
 }
 
-static void __exit drm_core_exit(void)
-{
-	debugfs_remove(drm_debugfs_root);
-	drm_sysfs_destroy();
-
-	unregister_chrdev(DRM_MAJOR, "drm");
-
-	drm_connector_ida_destroy();
-	idr_destroy(&drm_minors_idr);
-}
-
 module_init(drm_core_init);
 module_exit(drm_core_exit);