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: commit 975b9798be77b30cbed485583d0ccb48318708f7 Author: Chris Wilson <chris@chris-wilson.co.uk> Date: Wed May 21 08:58:24 2014 +0100 sna: Add support for Present Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Now I recompiled the intel driver with --disabled-dri3, and that fixes the issue also. My hardware 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.
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