drm/atomic: Add connector atomic_check function, v2.

The atomic_check function is useful for implementing properties, but
it can be used for other connector modeset related checks as well.

Similar to plane check functions, on a modeset atomic_check() is always
called.

Changes since v1:
- Make sure atomic_check() is called on any modeset.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1491477543-31257-5-git-send-email-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/drm_atomic_helper.c

@@ -459,10 +459,20 @@ mode_fixup(struct drm_atomic_state *state)
  *
  * Check the state object to see if the requested state is physically possible.
  * This does all the crtc and connector related computations for an atomic
- * update and adds any additional connectors needed for full modesets and calls
+ * update and adds any additional connectors needed for full modesets. It calls
- * down into &drm_crtc_helper_funcs.mode_fixup and
+ * the various per-object callbacks in the follow order:
- * &drm_encoder_helper_funcs.mode_fixup or
+ *
- * &drm_encoder_helper_funcs.atomic_check functions of the driver backend.
+ * 1. &drm_connector_helper_funcs.atomic_best_encoder for determining the new encoder.
+ * 2. &drm_connector_helper_funcs.atomic_check to validate the connector state.
+ * 3. If it's determined a modeset is needed then all connectors on the affected crtc
+ *    crtc are added and &drm_connector_helper_funcs.atomic_check is run on them.
+ * 4. &drm_bridge_funcs.mode_fixup is called on all encoder bridges.
+ * 5. &drm_encoder_helper_funcs.atomic_check is called to validate any encoder state.
+ *    This function is only called when the encoder will be part of a configured crtc,
+ *    it must not be used for implementing connector property validation.
+ *    If this function is NULL, &drm_atomic_encoder_helper_funcs.mode_fixup is called
+ *    instead.
+ * 6. &drm_crtc_helper_funcs.mode_fixup is called last, to fix up the mode with crtc constraints.
  *
  * &drm_crtc_state.mode_changed is set when the input mode is changed.
  * &drm_crtc_state.connectors_changed is set when a connector is added or
@@ -492,6 +502,7 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 	struct drm_connector *connector;
 	struct drm_connector_state *old_connector_state, *new_connector_state;
 	int i, ret;
+	unsigned connectors_mask = 0;
 
 	for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
 		bool has_connectors =
@@ -538,6 +549,8 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 		return ret;
 
 	for_each_oldnew_connector_in_state(state, connector, old_connector_state, new_connector_state, i) {
+		const struct drm_connector_helper_funcs *funcs = connector->helper_private;
+
 		/*
 		 * This only sets crtc->connectors_changed for routing changes,
 		 * drivers must set crtc->connectors_changed themselves when
@@ -555,6 +568,13 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 			    new_connector_state->link_status)
 				new_crtc_state->connectors_changed = true;
 		}
+
+		if (funcs->atomic_check)
+			ret = funcs->atomic_check(connector, new_connector_state);
+		if (ret)
+			return ret;
+
+		connectors_mask += BIT(i);
 	}
 
 	/*
@@ -581,6 +601,22 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 			return ret;
 	}
 
+	/*
+	 * Iterate over all connectors again, to make sure atomic_check()
+	 * has been called on them when a modeset is forced.
+	 */
+	for_each_oldnew_connector_in_state(state, connector, old_connector_state, new_connector_state, i) {
+		const struct drm_connector_helper_funcs *funcs = connector->helper_private;
+
+		if (connectors_mask & BIT(i))
+			continue;
+
+		if (funcs->atomic_check)
+			ret = funcs->atomic_check(connector, new_connector_state);
+		if (ret)
+			return ret;
+	}
+
 	return mode_fixup(state);
 }
 EXPORT_SYMBOL(drm_atomic_helper_check_modeset);

include/drm/drm_modeset_helper_vtables.h

@@ -872,6 +872,40 @@ struct drm_connector_helper_funcs {
 	 */
 	struct drm_encoder *(*atomic_best_encoder)(struct drm_connector *connector,
 						   struct drm_connector_state *connector_state);
+
+	/**
+	 * @atomic_check:
+	 *
+	 * This hook is used to validate connector state. This function is
+	 * called from &drm_atomic_helper_check_modeset, and is called when
+	 * a connector property is set, or a modeset on the crtc is forced.
+	 *
+	 * Because &drm_atomic_helper_check_modeset may be called multiple times,
+	 * this function should handle being called multiple times as well.
+	 *
+	 * This function is also allowed to inspect any other object's state and
+	 * can add more state objects to the atomic commit if needed. Care must
+	 * be taken though to ensure that state check and compute functions for
+	 * these added states are all called, and derived state in other objects
+	 * all updated. Again the recommendation is to just call check helpers
+	 * until a maximal configuration is reached.
+	 *
+	 * NOTE:
+	 *
+	 * This function is called in the check phase of an atomic update. The
+	 * driver is not allowed to change anything outside of the free-standing
+	 * state objects passed-in or assembled in the overall &drm_atomic_state
+	 * update tracking structure.
+	 *
+	 * RETURNS:
+	 *
+	 * 0 on success, -EINVAL if the state or the transition can't be
+	 * supported, -ENOMEM on memory allocation failure and -EDEADLK if an
+	 * attempt to obtain another state object ran into a &drm_modeset_lock
+	 * deadlock.
+	 */
+	int (*atomic_check)(struct drm_connector *connector,
+			    struct drm_connector_state *state);
 };
 
 /**