drm/atomic-helper: Add helper drm_atomic_helper_check_crtc_state()

Add drm_atomic_helper_check_crtc_state(), which contains tests common
to many CRTCs. The first added test verifies that an enabled CRTC has
at least one enabled primary plane.

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_atomic_helper.c

···
 EXPORT_SYMBOL(drm_atomic_helper_check_plane_state);
 
 /**
+ * drm_atomic_helper_check_crtc_state() - Check CRTC state for validity
+ * @crtc_state: CRTC state to check
+ * @can_disable_primary_planes: can the CRTC be enabled without a primary plane?
+ *
+ * Checks that a desired CRTC update is valid. Drivers that provide
+ * their own CRTC handling rather than helper-provided implementations may
+ * still wish to call this function to avoid duplication of error checking
+ * code.
+ *
+ * Note that @can_disable_primary_planes only tests if the CRTC can be
+ * enabled without a primary plane. To test if a primary plane can be updated
+ * without a CRTC, use drm_atomic_helper_check_plane_state() in the plane's
+ * atomic check.
+ *
+ * RETURNS:
+ * Zero if update appears valid, error code on failure
+ */
+int drm_atomic_helper_check_crtc_state(struct drm_crtc_state *crtc_state,
+				       bool can_disable_primary_planes)
+{
+	struct drm_device *dev = crtc_state->crtc->dev;
+	struct drm_atomic_state *state = crtc_state->state;
+
+	if (!crtc_state->enable)
+		return 0;
+
+	/* needs at least one primary plane to be enabled */
+	if (!can_disable_primary_planes) {
+		bool has_primary_plane = false;
+		struct drm_plane *plane;
+
+		drm_for_each_plane_mask(plane, dev, crtc_state->plane_mask) {
+			struct drm_plane_state *plane_state;
+
+			if (plane->type != DRM_PLANE_TYPE_PRIMARY)
+				continue;
+			plane_state = drm_atomic_get_plane_state(state, plane);
+			if (IS_ERR(plane_state))
+				return PTR_ERR(plane_state);
+			if (plane_state->fb && plane_state->crtc) {
+				has_primary_plane = true;
+				break;
+			}
+		}
+		if (!has_primary_plane) {
+			drm_dbg_kms(dev, "Cannot enable CRTC without a primary plane.\n");
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_atomic_helper_check_crtc_state);
+
+/**
  * drm_atomic_helper_check_planes - validate state object for planes changes
  * @dev: DRM device
  * @state: the driver state object

include/drm/drm_atomic_helper.h

···
 					int max_scale,
 					bool can_position,
 					bool can_update_disabled);
+int drm_atomic_helper_check_crtc_state(struct drm_crtc_state *crtc_state,
+				       bool can_disable_primary_plane);
 int drm_atomic_helper_check_planes(struct drm_device *dev,
 			       struct drm_atomic_state *state);
 int drm_atomic_helper_check(struct drm_device *dev,