Mutter shows black screen on the external monitor
Affected version
- Fedora 31
- Kernel version is 5.4.10, but older versions are affected as well. I can't find a version that is not affected by the problem.
- Mutter 3.34.3
- !1007 (merged) and !1010 (merged) are applied to fix mutter crash. Please see #917 (closed) for more information.
- Both XOrg and Wayland are broken
- It is a regression for Wayland mode. Mutter 3.32 works fine on the same hardware.
- It is not a regression for XOrg mode. Mutter 3.32 is already broken on XOrg.
Bug summary
Mutter is able to detect the external monitor, but it always shows a black screen on it. I can move a window to the external monitor, but doing so makes the window invisible except for the mouse pointer.
Steps to reproduce
- Plug in an HDMI cable attached to an external monitor on an affected laptop.
- Open gnome-control-center to confirm it is detected properly.
What happened
Mutter 3.34 just shows black screen on the external monitor. Nothing is visible except for the mouse pointer.
What did you expect to happen
Mutter 3.34 should allow me to use the external monitor like mutter 3.32.
Relevant logs, screenshots, screencasts etc.
Please see dmesg log in #917 (comment 687839) and #917 (comment 664934). On mutter 3.32, the kernel prints nothing. On mutter 3.34, the kernel prints a lot of call traces. The builtin monitor uses i915 and the external monitor uses nouveau. It is not possible to use an external monitor without nouveau on the laptop. If I blacklist nouveau on boot, the external monitor can't be detected.