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

[Cedric M]

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

[Daniel van Vugt (vanvugt)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. This particular bug has already been reported and is a duplicate of bug 1626935, so it is being marked as such. Please look at the other bug report to see if there is any missing information that you can provide, or to see if there is a workaround for the bug. Additionally, any further discussion regarding the bug should occur in the other report. Feel free to continue to report any other bugs you may find.

[Cedric M (cedric-m)]

Hi,

Doesn't looks like a duplicate of bug 1626935 to me!

The flickering in my case happens:
- only when something light happens in somewhere on the external screen (like entering a single character in a terminal window). When nothing happens on screen, or when using graphics-heavier apps (like a web browser), the screen doesn't flicker
- the flickering is not similar to a triple buffering issue neither is related to the nautilus wallpaper -- it looks like a DisplayPort reset (ie, as if you disconnect/reconnect the monitor), with a 2-3s complete blackout of the monitor
- this is specific to the modesetting driver. The xserver-xorg-video-intel driver is fine.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Nicolas Ramoudt (smoetje)]

After a long search for many many weeks/months, I have found this post. I own a Lenovo T550 and tried different versions of Ubuntu's, to connect to my 2 external Asus PB279Q (4K) via Displayport (1.2). Tried as well via the docking-station and the DP in the laptop itself (connecting both gives me dual 4K @60hz :). Tried monitors also separately/alone, same issue with *exactly the same symptoms* like described here above. Yesterday found, I even downloaded and tried the latest 17.04 (Beta 2), issue is still present.

The screen flickering is random (goes completely black for a few seconds) doing normal browsing work, study, etc. But the blinking considerably occurs much more often, when the terminal window is open. It appears to be occuring depending of the type of content being displayed (e.g. when using phpstorm in 'darcula' mode, it also occurs more). It appears the displayport suddenly goes haywire and switches back.
Lowering working-resolution to 2560x1440 and the issue appears to be vanished.

I tried as well with the default (standard) driver, as well with the ones I found and installed from 01.org.

I work with Ubuntu on user-level, developing web apps. I am handling myself, never did reported these issues, so this is new to me. But since we searched for such a long time without solution found, almost reaching the limits of our patience, I think it's about time and worth to report... (hoping one day for a fix/solution)

I know more or less how to reproduce the issue (although it's random, sometimes I need patience, I can let it 'trigger' more quickly), my feedback may be of any help? If there's some kind of instructions I can follow how to pull out relevant logs (I'm not noob, but also not yet a guru...)
I can try to pull them out and post them here if wished/required.

[Cedric M (cedric-m)]

Hey

The issue has just been solved for me in the "work in progress" Intel kernel branch (drm-tip).

Try a kernel here: http://kernel.ubuntu.com/~kernel-ppa/mainline/drm-tip/

I hope that those fixes will be included in kernel 4.12.

[Nicolas Ramoudt (smoetje)]

Hi

Working for 2 days now on Ubuntu 17.04, updated to your proposed kernel 4.11.0-994
Amazing... working dual 4K now via 2x displayport 1.2 without a glitch on both monitors for the first time.

Fantastic! And indeed, I hope too, that these fixes will be included a.s.a.p.
I was almost desperate here...

Your solution-proposal really saved my day, so thanks a lot!

[Cedric M (cedric-m)]

Glad it worked for you too.

The guys who did the actual work are the one to be thanked ;)

Now let's see when this gets merged in mainline & stock Ubuntu kernels!

[Timo Aaltonen (tjaalton)]

should get mainline in 4.12, so 17.10 unless the commit(s) get backported