I recently upgraded my system to Ubuntu 14.10.
Now when testing HDMI, I hit some bug.
My system is an optimus laptop.
The HDMI is connected to a nvidia card.
Now the HDMI has signal, and while logging in (so when Xorg is starting) I can shortly move my cursor over the external display. But when login is complete, the external display is 1 artifact, and doesn't show any updates anymore.
So I started bisecting the version from 14.10 to 14.04 (where it was working).
And I found out the following commit caused the issue:
Author: Chris Wilson <email@example.com>
Date: Wed May 21 08:58:24 2014 +0100
sna: Add support for Present
Signed-off-by: Chris Wilson <firstname.lastname@example.org>
Now I recompiled the intel driver with --disabled-dri3, and that fixes the issue also.
00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
01:00.0 VGA compatible controller: NVIDIA Corporation GF108M [GeForce GT 540M] (rev a1)
The driver I use for the nvidia card is nouveau.
Please re-test with a current server and reopen if this is still an issue for you.