drm/tests: managed: Add comments about test intent

Add comments explaining the intention behind the test and certain
implementation details related to device lifetime.
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240115171351.504264-4-michal.winiarski@intel.com

drivers/gpu/drm/tests/drm_managed_test.c

@@ -24,6 +24,10 @@ static void drm_action(struct drm_device *drm, void *ptr)
 	wake_up_interruptible(&priv->action_wq);
 }
 
+/*
+ * The test verifies that the release action is called automatically when the
+ * device is released.
+ */
 static void drm_test_managed_run_action(struct kunit *test)
 {
 	struct managed_test_priv *priv;
@@ -38,6 +42,11 @@ static void drm_test_managed_run_action(struct kunit *test)
 	dev = drm_kunit_helper_alloc_device(test);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dev);
 
+	/*
+	 * DRM device can't be embedded in priv, since priv->action_done needs
+	 * to remain allocated beyond both parent device and drm_device
+	 * lifetime.
+	 */
 	drm = __drm_kunit_helper_alloc_drm_device(test, dev, sizeof(*drm), 0, DRIVER_MODESET);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, drm);