Created attachment 132664 [details]
The same hardware as for https://bugs.freedesktop.org/show_bug.cgi?id=101764
When the HDMI cable is connected there is no signal for the external monitor and the internal panel keeps working as expected.
The journal when the cable is attached and then detached is attached to this ticket. What's interesting to me is:
gdm-Xorg-:0: (EE) NOUVEAU(G0): failed to set mode: No space left on device
Created attachment 132665 [details]
Created attachment 132666 [details]
xrandr output before attaching the HDMI cable
Created attachment 132667 [details]
xrandr output after attaching the HDMI cable
Apparently the problem is:
(EE) NOUVEAU(G0): Error creating GPU channel: -19
(EE) NOUVEAU(G0): Error initialising acceleration. Falling back to NoAccel
in our kernel we are booting with 'noaccel=1' that is disabling acceleration. But nouveau can't do the prime offload without accel since it uses the copy engine to copy the framebuffer out.