Public bug reported:

Hi,

I'm using a Dell XPS 13 (9343 // i7-5600U broadwell, 3200x1800 panel)
laptop, directly attached to an external Dell P2715Q 4K (3840x2160
@60Hz) via DP.

The 4K external screen is flickering when doing light activity -- easily
reproduced when using an X terminal.

Steps to reproduce:
- open side by side Firefox (or Chrome) + a terminal and/or a gvim window on 
the external 4K screen
- do some light web browsing
- give focus to the X terminal or gvim
  // at this point, display is still perfectly steady
- press a key to enter a single character
  // as soon as the key is pressed, external screen goes black for a few 
seconds. Laptop screen is not affected.
- Wait for the screen to come back, then continue typing
  // screen generally stays ON, but sometimes continues to flicker a few times 
in next minute.

This happens almost every time I switch to the terminal window and start
typing.

OS specs:
- Ubuntu 16.10 running Unity, modesetting Xorg driver
- kernel 4.8.0. Issue is still present with 4.9.0rc1.

The intel driver (cp /usr/share/doc/xserver-xorg-video-intel/xorg.conf
/etc/X11) doesn't exhibit this issue.


Also reported upstream: https://bugs.freedesktop.org/show_bug.cgi?id=97264

** Affects: xorg-server (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1636486

Title:
  External screen flickers (esp. in terminals) with xorg modesetting
  driver on Intel Broadwell

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