drm/amd/display: Avoid full modeset when not required

Fix IGT test case (kms_atomic_transition)
-DRM sets the mode_changed flag, while we don't need to do a full
 modeset.
-We want to override the mode_changed flag in this case

If we don't do this, we will still bypass the modeset in DC. This will
fail to update the new stream_status, causing nullptr at a later stage
when trying to access stream_status"

We now avoid this by discarding the new_stream instead of partially
filling it.
Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -1608,8 +1608,16 @@ struct dm_connector_state {
 #define to_dm_connector_state(x)\
 	container_of((x), struct dm_connector_state, base)
 
-static bool modeset_required(struct drm_crtc_state *crtc_state)
+static bool modeset_required(struct drm_crtc_state *crtc_state,
+			     struct dc_stream *new_stream,
+			     struct dc_stream *old_stream)
 {
+	if (dc_is_stream_unchanged(new_stream, old_stream)) {
+		crtc_state->mode_changed = false;
+		DRM_DEBUG_KMS("Mode change not required, setting mode_changed to %d",
+			      crtc_state->mode_changed);
+	}
+
 	if (!drm_atomic_crtc_needs_modeset(crtc_state))
 		return false;
 
@@ -2904,7 +2912,8 @@ static int dm_crtc_helper_atomic_check(
 	struct dm_crtc_state *dm_crtc_state = to_dm_crtc_state(state);
 	int ret = -EINVAL;
 
-	if (unlikely(!dm_crtc_state->stream && modeset_required(state))) {
+	if (unlikely(!dm_crtc_state->stream &&
+		     modeset_required(state, NULL, dm_crtc_state->stream))) {
 		WARN_ON(1);
 		return ret;
 	}
@@ -4087,7 +4096,7 @@ void amdgpu_dm_atomic_commit_tail(
 		 * aconnector as needed
 		 */
 
-		if (modeset_required(new_state)) {
+		if (modeset_required(new_state, new_acrtc_state->stream, old_acrtc_state->stream)) {
 
 			DRM_INFO("Atomic commit: SET crtc id %d: [%p]\n", acrtc->crtc_id, acrtc);
 
@@ -4536,6 +4545,9 @@ int amdgpu_dm_atomic_check(struct drm_device *dev,
 	for_each_crtc_in_state(state, crtc, crtc_state, i) {
 		struct amdgpu_crtc *acrtc = NULL;
 		struct amdgpu_connector *aconnector = NULL;
+		struct dc_stream *new_stream = NULL;
+		struct drm_connector_state *conn_state = NULL;
+		struct dm_connector_state *dm_conn_state = NULL;
 
 		old_acrtc_state = to_dm_crtc_state(crtc->state);
 		new_acrtc_state = to_dm_crtc_state(crtc_state);
@@ -4555,23 +4567,50 @@ int amdgpu_dm_atomic_check(struct drm_device *dev,
 			crtc_state->active_changed,
 			crtc_state->connectors_changed);
 
-		if (modeset_required(crtc_state)) {
+		if (modereset_required(crtc_state)) {
 
-			struct dc_stream *new_stream = NULL;
-			struct drm_connector_state *conn_state = NULL;
-			struct dm_connector_state *dm_conn_state = NULL;
+					/* i.e. reset mode */
+			if (new_acrtc_state->stream) {
+				set_count = remove_from_val_sets(
+						set,
+						set_count,
+						new_acrtc_state->stream);
+
+				dc_stream_release(new_acrtc_state->stream);
+				new_acrtc_state->stream = NULL;
+
+				lock_and_validation_needed = true;
+			}
+
+		} else {
 
 			if (aconnector) {
-				conn_state = drm_atomic_get_connector_state(state, &aconnector->base);
+				conn_state = drm_atomic_get_connector_state(state,
+									    &aconnector->base);
+
 				if (IS_ERR(conn_state)) {
 					ret = PTR_ERR_OR_ZERO(conn_state);
 					goto fail;
 				}
 
 				dm_conn_state = to_dm_connector_state(conn_state);
+
+				new_stream = create_stream_for_sink(aconnector,
+								    &crtc_state->mode,
+								    dm_conn_state);
+
+				if (!new_stream) {
+					DRM_DEBUG_KMS("%s: Failed to create new stream for crtc %d\n",
+							__func__, acrtc->base.base.id);
+					break;
 				}
 
-			new_stream = create_stream_for_sink(aconnector, &crtc_state->mode, dm_conn_state);
+
+			}
+
+			if (modeset_required(crtc_state, new_stream,
+					     old_acrtc_state->stream)) {
+
 
 			/*
 			 * we can have no stream on ACTION_SET if a display
@@ -4579,11 +4618,6 @@ int amdgpu_dm_atomic_check(struct drm_device *dev,
 			 * error, the OS will be updated after detection, and
 			 * do the right thing on next atomic commit
 			 */
-			if (!new_stream) {
-				DRM_DEBUG_KMS("%s: Failed to create new stream for crtc %d\n",
-						__func__, acrtc->base.base.id);
-				break;
-			}
 
 				if (new_acrtc_state->stream)
 					dc_stream_release(new_acrtc_state->stream);
@@ -4598,20 +4632,13 @@ int amdgpu_dm_atomic_check(struct drm_device *dev,
 						crtc);
 
 				lock_and_validation_needed = true;
+			} else {
+				/*
+				 * The new stream is unused, so we release it
+				 */
+				if (new_stream)
+					dc_stream_release(new_stream);
 
-		} else if (modereset_required(crtc_state)) {
-
-			/* i.e. reset mode */
-			if (new_acrtc_state->stream) {
-				set_count = remove_from_val_sets(
-						set,
-						set_count,
-						new_acrtc_state->stream);
-
-				dc_stream_release(new_acrtc_state->stream);
-				new_acrtc_state->stream = NULL;
-
-				lock_and_validation_needed = true;
 			}
 		}