drm/vc4: tests: Add function to lookup a plane for a CRTC

Some tests will need to find a plane to run a test on for a given CRTC.
Let's create a small helper to do that.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>

Author: mripard

drivers/gpu/drm/vc4/tests/vc4_mock.h

@@ -21,6 +21,24 @@ struct drm_crtc *vc4_find_crtc_for_encoder(struct kunit *test,
 	return NULL;
 }
 
+static inline
+struct drm_plane *vc4_mock_find_plane_for_crtc(struct kunit *test,
+					       struct drm_crtc *crtc)
+{
+	struct drm_device *drm = crtc->dev;
+	struct drm_plane *plane;
+
+	drm_for_each_plane(plane, drm)
+		if (plane->possible_crtcs & drm_crtc_mask(crtc))
+			return plane;
+
+	return NULL;
+}
+
+struct vc4_dummy_plane {
+	struct vc4_plane plane;
+};
+
 struct drm_plane *vc4_dummy_plane(struct kunit *test, struct drm_device *drm,
 				  enum drm_plane_type type);