backend/drm: track cursor FB in wlr_drm_connector_state

Use the same logic for cursor FBs as we currently use for primary
FBs. This also fixes the same bug as [1] but in a different, more
robust way.

The new logic integrates better with atomic and will be required
anyways in the future when set_cursor will be superseded by a better
API.

[1]: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/4577

backend/drm/atomic.c

@@ -362,7 +362,7 @@ static bool atomic_crtc_commit(struct wlr_drm_connector *conn,
 		}
 		if (crtc->cursor) {
 			if (drm_connector_is_cursor_visible(conn)) {
-				set_plane_props(&atom, drm, crtc->cursor, get_next_cursor_fb(conn),
+				set_plane_props(&atom, drm, crtc->cursor, state->cursor_fb,
 					crtc->id, conn->cursor_x, conn->cursor_y);
 			} else {
 				plane_disable(&atom, crtc->cursor);

backend/drm/drm.c

@@ -468,9 +468,10 @@ static bool drm_crtc_commit(struct wlr_drm_connector *conn,
 	bool ok = drm->iface->crtc_commit(conn, state, page_flip, flags, test_only);
 	if (ok && !test_only) {
 		drm_fb_copy(&crtc->primary->queued_fb, state->primary_fb);
-		if (crtc->cursor != NULL && conn->cursor_pending_fb != NULL) {
+		if (crtc->cursor != NULL) {
-			drm_fb_move(&crtc->cursor->queued_fb, &conn->cursor_pending_fb);
+			drm_fb_copy(&crtc->cursor->queued_fb, state->cursor_fb);
 		}
+		drm_fb_clear(&conn->cursor_pending_fb);
 
 		struct wlr_drm_layer *layer;
 		wl_list_for_each(layer, &crtc->layers, link) {
@@ -551,10 +552,21 @@ static void drm_connector_state_init(struct wlr_drm_connector_state *state,
 			state->primary_fb = drm_fb_lock(primary->current_fb);
 		}
 	}
+	if (conn->crtc != NULL && conn->cursor_enabled) {
+		struct wlr_drm_plane *cursor = conn->crtc->cursor;
+		if (conn->cursor_pending_fb != NULL) {
+			state->cursor_fb = drm_fb_lock(conn->cursor_pending_fb);
+		} else if (cursor->queued_fb != NULL) {
+			state->cursor_fb = drm_fb_lock(cursor->queued_fb);
+		} else if (cursor->current_fb != NULL) {
+			state->cursor_fb = drm_fb_lock(cursor->current_fb);
+		}
+	}
 }
 
 static void drm_connector_state_finish(struct wlr_drm_connector_state *state) {
 	drm_fb_clear(&state->primary_fb);
+	drm_fb_clear(&state->cursor_fb);
 }
 
 static bool drm_connector_state_update_primary_fb(struct wlr_drm_connector *conn,
@@ -877,19 +889,6 @@ static size_t drm_connector_get_gamma_size(struct wlr_output *output) {
 	return drm_crtc_get_gamma_lut_size(drm, crtc);
 }
 
-struct wlr_drm_fb *get_next_cursor_fb(struct wlr_drm_connector *conn) {
-	if (!conn->cursor_enabled || conn->crtc == NULL) {
-		return NULL;
-	}
-	if (conn->cursor_pending_fb != NULL) {
-		return conn->cursor_pending_fb;
-	}
-	if (conn->crtc->cursor->queued_fb != NULL) {
-		return conn->crtc->cursor->queued_fb;
-	}
-	return conn->crtc->cursor->current_fb;
-}
-
 static void realloc_crtcs(struct wlr_drm_backend *drm,
 	struct wlr_drm_connector *want_conn);
 

backend/drm/legacy.c

@@ -134,7 +134,7 @@ static bool legacy_crtc_commit(struct wlr_drm_connector *conn,
 	}
 
 	if (cursor != NULL && drm_connector_is_cursor_visible(conn)) {
-		struct wlr_drm_fb *cursor_fb = get_next_cursor_fb(conn);
+		struct wlr_drm_fb *cursor_fb = state->cursor_fb;
 		if (cursor_fb == NULL) {
 			wlr_drm_conn_log(conn, WLR_DEBUG, "Failed to acquire cursor FB");
 			return false;

backend/drm/libliftoff.c

@@ -419,7 +419,7 @@ static bool crtc_commit(struct wlr_drm_connector *conn,
 		if (crtc->cursor) {
 			if (drm_connector_is_cursor_visible(conn)) {
 				ok = ok && set_plane_props(crtc->cursor, crtc->cursor->liftoff_layer,
-					get_next_cursor_fb(conn), conn->cursor_x, conn->cursor_y,
+					state->cursor_fb, conn->cursor_x, conn->cursor_y,
 					wl_list_length(&crtc->layers) + 1);
 			} else {
 				ok = ok && disable_plane(crtc->cursor);

include/backend/drm/drm.h

@@ -129,6 +129,7 @@ struct wlr_drm_connector_state {
 	bool active;
 	drmModeModeInfo mode;
 	struct wlr_drm_fb *primary_fb;
+	struct wlr_drm_fb *cursor_fb;
 };
 
 /**
@@ -196,7 +197,6 @@ size_t drm_crtc_get_gamma_lut_size(struct wlr_drm_backend *drm,
 void drm_lease_destroy(struct wlr_drm_lease *lease);
 void drm_page_flip_destroy(struct wlr_drm_page_flip *page_flip);
 
-struct wlr_drm_fb *get_next_cursor_fb(struct wlr_drm_connector *conn);
 struct wlr_drm_layer *get_drm_layer(struct wlr_drm_backend *drm,
 	struct wlr_output_layer *layer);