On Intel systems when the X server exits the display is turned off and remains off. This is triggered when using LightDM and switching to a greeter (starts a second X server) then authenticating in that greeter and returning to the first X server (the greeter X server is stopped).
The cause seems to be a DPMS change from bug 90179 (revision 7d9a74622e5a936e4860fcef8358619bf59adae8) that causes the driver to turn off the output if DPMS is not working.
Tracked in Launchpad:
We are currently working around this issue in Ubuntu 15.04 by reverting that one commmit.
(In reply to Robert Ancell from comment #1)
> We are currently working around this issue in Ubuntu 15.04 by reverting that
> one commmit.
That one commit being
Author: Chris Wilson <email address hidden>
Date: Mon Jun 15 14:16:34 2015 +0100
sna: Be robust in handling DPMS failures
i.e. not a kernel commit. Apparently Chris' conclusion was that the kernel returns an error on DPMS.
Please attach dmesg with drm.debug=14 module parameter, all the way from boot to reproducing the problem.
I haven't been able to generate a dmesg due to another kernel issue I have where it spams the log. I will generate one when that issue is resolved...
This bug is really old, is this problem still persist? Robert are you able now to share your dmesg?
Closing this issue due to age/inactivity and missing information to proceed.
Robert if you still face with issue with latest kernel, please reopen the issue and attached all necessary information (here is useful info to collect these data: https://01.org/linuxgraphics/documentation/bugs-and-debugging)