output-management: work around wlroots crash

river/Root.zig

@@ -770,6 +770,17 @@ fn processOutputConfig(
         var proposed_state = wlr.Output.State.init();
         head.state.apply(&proposed_state);
 
+        // Work around a division by zero in the wlroots drm backend.
+        // See https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3791
+        // TODO(wlroots) remove this workaround after 0.17.2 is out.
+        if (output.wlr_output.isDrm() and
+            proposed_state.committed.mode and
+            proposed_state.mode_type == .custom and
+            proposed_state.custom_mode.refresh == 0)
+        {
+            proposed_state.custom_mode.refresh = 60000;
+        }
+
         switch (action) {
             .test_only => {
                 if (!wlr_output.testState(&proposed_state)) success = false;