Comment 26 for bug 1173491

Ahhh, given what you just mentioned, I remembered that I had added a line to /etc/lightdm/lightdm.conf, in order to force light-dm to use the native resoltution of the display:

display-setup-script=xrandr --output HDMI2 --primary --mode 1440x900

This was returning a failure code, causing light-dm to terminate.

The reason for this, in turn, appears to be that the native resolution is no longer being detected at all!

Upon lgging into my graphical session I was greeted by a bad resulution and a very long error dialog box, spanning multiple screens (text attached). I am unable to select the native resolution, which leaves me with cropped display output.

I guess this means that the original issue was effectively my fault, although it stems from the underlying issue that the supported modes are no longer being detected correctly. Of course it is still possible that this is due to bad EDID info from the display, but the fact remains that the older kernel is able to drive the display at its native resolution.

(The reason the log was missing from my uploads was presumably because I didn't think apport needed to run as root. As it turns out, the light-dm logs are only readable by root. Apport didn't warn me / complain about this, so I assumed everyting was fine.)