backend/drm: add wlr_drm_connector_state.nonblock

Instead of having this condition checked in multiple places,
centralize it so that they don't go out-of-sync.

backend/drm/atomic.c

@@ -315,12 +315,8 @@ static bool atomic_crtc_commit(struct wlr_drm_connector *conn,
 	}
 	if (modeset) {
 		flags |= DRM_MODE_ATOMIC_ALLOW_MODESET;
-	} else if (!test_only && (state->base->committed & WLR_OUTPUT_STATE_BUFFER)) {
-		// The wlr_output API requires non-modeset commits with a new buffer to
-		// wait for the frame event. However compositors often perform
-		// non-modesets commits without a new buffer without waiting for the
-		// frame event. In that case we need to make the KMS commit blocking,
-		// otherwise the kernel will error out with EBUSY.
+	}
+	if (!test_only && state->nonblock) {
 		flags |= DRM_MODE_ATOMIC_NONBLOCK;
 	}
 

backend/drm/drm.c

@@ -489,6 +489,13 @@ static void drm_connector_state_init(struct wlr_drm_connector_state *state,
 		.modeset = base->allow_reconfiguration,
 		.active = (base->committed & WLR_OUTPUT_STATE_ENABLED) ?
 			base->enabled : conn->output.enabled,
+		// The wlr_output API requires non-modeset commits with a new buffer to
+		// wait for the frame event. However compositors often perform
+		// non-modesets commits without a new buffer without waiting for the
+		// frame event. In that case we need to make the KMS commit blocking,
+		// otherwise the kernel will error out with EBUSY.
+		.nonblock = !base->allow_reconfiguration &&
+			(base->committed & WLR_OUTPUT_STATE_BUFFER),
 	};
 
 	struct wlr_output_mode *mode = conn->output.current_mode;
@@ -763,16 +770,6 @@ bool drm_connector_commit_state(struct wlr_drm_connector *conn,
 		if (!drm_connector_state_update_primary_fb(conn, &pending)) {
 			goto out;
 		}
-
-		// wlr_drm_interface.crtc_commit will perform either a non-blocking
-		// page-flip, either a blocking modeset. When performing a blocking modeset
-		// we'll wait for all queued page-flips to complete, so we don't need this
-		// safeguard.
-		if (conn->pending_page_flip != NULL && !pending.modeset) {
-			wlr_drm_conn_log(conn, WLR_ERROR, "Failed to page-flip output: "
-				"a page-flip is already pending");
-			goto out;
-		}
 	}
 	if (pending.base->committed & WLR_OUTPUT_STATE_LAYERS) {
 		if (!drm_connector_set_pending_layer_fbs(conn, pending.base)) {
@@ -790,6 +787,16 @@ bool drm_connector_commit_state(struct wlr_drm_connector *conn,
 		}
 	}
 
+	// wlr_drm_interface.crtc_commit will perform either a non-blocking
+	// page-flip, either a blocking modeset. When performing a blocking modeset
+	// we'll wait for all queued page-flips to complete, so we don't need this
+	// safeguard.
+	if (pending.nonblock && conn->pending_page_flip != NULL) {
+		wlr_drm_conn_log(conn, WLR_ERROR, "Failed to page-flip output: "
+			"a page-flip is already pending");
+		goto out;
+	}
+
 	uint32_t flags = 0;
 	if (pending.active) {
 		flags |= DRM_MODE_PAGE_FLIP_EVENT;

backend/drm/libliftoff.c

@@ -368,12 +368,8 @@ static bool crtc_commit(struct wlr_drm_connector *conn,
 	}
 	if (modeset) {
 		flags |= DRM_MODE_ATOMIC_ALLOW_MODESET;
-	} else if (!test_only && (state->base->committed & WLR_OUTPUT_STATE_BUFFER)) {
-		// The wlr_output API requires non-modeset commits with a new buffer to
-		// wait for the frame event. However compositors often perform
-		// non-modesets commits without a new buffer without waiting for the
-		// frame event. In that case we need to make the KMS commit blocking,
-		// otherwise the kernel will error out with EBUSY.
+	}
+	if (!test_only && state->nonblock) {
 		flags |= DRM_MODE_ATOMIC_NONBLOCK;
 	}
 

include/backend/drm/drm.h

@@ -126,6 +126,7 @@ struct wlr_drm_mode {
 struct wlr_drm_connector_state {
 	const struct wlr_output_state *base;
 	bool modeset;
+	bool nonblock;
 	bool active;
 	drmModeModeInfo mode;
 	struct wlr_drm_fb *primary_fb;