Public bug reported:
Steps:
1. Install trusty image and log in to system
2. Connect an external DP monitor.
3. Press the display hot key to change the monitors configuration
Actual result:
Split screen after set the monitors configuration to extended mode.
Expected result:
The video signal can be mirrored, extended, displayed on external or onboard
only.
[Analysis from NVIDIA]
I tracked down the culprit to an Ubuntu patch applied to xf86-video-intel
2.99.910: patches/10-handle-rotated-slaves.diff. That patch is a cherry-pick of
upstream commit a45b2ea11c15f35c36330ff27cb45854a29c2e2c. The Ubuntu version of
the patch is significantly different from the upstream commit, so somebody must
have done quite a bit of porting. Either they messed it up during porting, or
they missed cherry-picking another upstream commit that fixes the problem.
It looks like what's happening is that the Intel driver is applying the
RandR CRTC offset even though it's actually scanning out from a CRTC-
sized private scanout buffer. Since it's a linear buffer, this shifts
all of the lines over by however many pixels the CRTC offset is set to,
wrapping lines around in the process.
** Affects: xorg-server (Ubuntu)
Importance: High
Status: New
** Attachment added: "screenshot of the issue"
https://bugs.launchpad.net/bugs/1405325/+attachment/4286777/+files/IMG_20141208_141739.jpg
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https://bugs.launchpad.net/bugs/1405325
Title:
[I+N] Split screen after setting the monitors configuration to
extended
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