drm/simple-kms: Use drm_atomic_helper_check_crtc_state()

Simple-KMS helpers guarantee that the CRTC and plane enable
flags are synchronized. Implement this with atomic helpers
drm_atomic_helper_check_crtc_state() on the CRTC side, and
drm_atomic_helper_check_plane_state() on the plane side.

Signed-off-by: Thomas Zimmermann <[e-mail]>
Acked-by: Jocelyn Falempe <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_simple_kms_helper.c

···
 static int drm_simple_kms_crtc_check(struct drm_crtc *crtc,
 				     struct drm_atomic_state *state)
 {
-	struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state,
-									  crtc);
-	bool has_primary = crtc_state->plane_mask &
-			   drm_plane_mask(crtc->primary);
+	struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
+	int ret;
 
-	/* We always want to have an active plane with an active CRTC */
-	if (has_primary != crtc_state->enable)
-		return -EINVAL;
+	ret = drm_atomic_helper_check_crtc_state(crtc_state, false);
+	if (ret)
+		return ret;
 
 	return drm_atomic_add_affected_planes(state, crtc);
 }
···
 	ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
 						  DRM_PLANE_HELPER_NO_SCALING,
 						  DRM_PLANE_HELPER_NO_SCALING,
-						  false, true);
+						  false, false);
 	if (ret)
 		return ret;