drm/tests: helpers: Create kunit helper to destroy a drm_display_mode

A number of test suites call functions that expect the returned
drm_display_mode to be destroyed eventually.

However, none of the tests called drm_mode_destroy, which results in a
memory leak.

Since drm_mode_destroy takes two pointers as argument, we can't use a
kunit wrapper. Let's just create a helper every test suite can use.

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20250408-drm-kunit-drm-display-mode-memleak-v1-1-996305a2e75a@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

drivers/gpu/drm/tests/drm_kunit_helpers.c

@@ -278,6 +278,28 @@ static void kunit_action_drm_mode_destroy(void *ptr)
 	drm_mode_destroy(NULL, mode);
 }
 
+/**
+ * drm_kunit_add_mode_destroy_action() - Add a drm_destroy_mode kunit action
+ * @test: The test context object
+ * @mode: The drm_display_mode to destroy eventually
+ *
+ * Registers a kunit action that will destroy the drm_display_mode at
+ * the end of the test.
+ *
+ * If an error occurs, the drm_display_mode will be destroyed.
+ *
+ * Returns:
+ * 0 on success, an error code otherwise.
+ */
+int drm_kunit_add_mode_destroy_action(struct kunit *test,
+				      struct drm_display_mode *mode)
+{
+	return kunit_add_action_or_reset(test,
+					 kunit_action_drm_mode_destroy,
+					 mode);
+}
+EXPORT_SYMBOL_GPL(drm_kunit_add_mode_destroy_action);
+
 /**
  * drm_kunit_display_mode_from_cea_vic() - return a mode for CEA VIC for a KUnit test
  * @test: The test context object

include/drm/drm_kunit_helpers.h

@@ -118,6 +118,9 @@ drm_kunit_helper_create_crtc(struct kunit *test,
 			     const struct drm_crtc_funcs *funcs,
 			     const struct drm_crtc_helper_funcs *helper_funcs);
 
+int drm_kunit_add_mode_destroy_action(struct kunit *test,
+				      struct drm_display_mode *mode);
+
 struct drm_display_mode *
 drm_kunit_display_mode_from_cea_vic(struct kunit *test, struct drm_device *dev,
 				    u8 video_code);