Created attachment 121993 [details]
xrandr + OSD 139Hz

Hello,

I have Arch linux with an asus MG279Q (27 "144Hz) connected in DisplayPort 1.2. Everything worked with Sapphire 7950 and also R9 Fury. 
Unfortunately I have trouble with my Sapphire 290x. I've tested three 290X to be sure it's not an hardware issue. 
Of course freesync is off.
I just tested the combo with multiple users 290 (X and not X) + MG279Q. Sometimes on livecd. Everyone have the issue.

I can't have a real 144Hz with the amdgpu or radeon driver. Everything work only @60Hz or with FGLRX driver.
At 144Hz , i have a bad 139Hz with artifacts : http://reho.st/self/b98c1c955cb7d42c3af6f82ea71bbc94be8aee6a.jpg

Glitches on the left. Blur on all screen, Text glitches...

What i've tried :
- Windows 10 : All works !
- FGLRX : All works @144Hz. But other problems make it difficult to use: in firefox lag among others ... And I love the free driver! Finally ... When he worked with my 7950
- Kernel mainline : Same issue .
- New mode line with cvt 2560 1440 144 and xrandr --newmode : Same issue.
- Contact Sapphire and upload to a new vbios : Same issue and as long as it works on windows it's not their problem...

It can be an incompatibility between the MG279Q and the 290X on linux. But something in FGLRX make my 290X works, but not present on AMDGPU/Radeon driver.

I just tested the combo with multiple users 290 (X and not X) + MG279Q. Sometimes on livecd. Everyone have the issue.

Thanks for your help