Multimonitor does not work correctly with Modesetting driver on Intel hardware with xorg-server 1.19.99.902

Submitted by Michael Marley

Assigned to Xorg Project Team

Link to original bug (#105812)

Description

Created attachment 138436 Xorg.0.log from a reproduction of the issue

After upgrading from xserver 1.19.6 (the stock provided version) to 1.19.99.902 (a custom build) on a Kubuntu 18.04 x86_64 system, multimonitor support has ceased to work correctly. With the older version it worked as expected but with the newer version, even though the monitors are set to an extended desktop, the second monitor appears black until KDE starts and then is a clone of the first monitor, except the mouse cursor does not show on the second monitor at all. Attempting to change the display configuration using the KDE display configuration utility has no effect.

Both monitors are Dell U2312HM monitors connected to the computer by DisplayPort. The computer is a Lenovo ThinkCentre m900, which has a "Intel(R) HD Graphics 530 (Skylake GT2)" graphics device. The system is currently running Linux 4.16-rc7, though the kernel version does not have any apparent effect on the problem, nor does any useful information print in the kernel log.

I have attached the Xorg.0.log file, which contains the line "[ 228.979] (EE) modeset(0): failed to set mode: No space left on device" which I believe is related to the problem.

If I can provide any other data, please let me know.

Attachment 138436, "Xorg.0.log from a reproduction of the issue":
Xorg.0.log