AMD Richland (ARUBA) no screen at DP output when using three displays

Submitted by Balázs Vinarz

Assigned to Default DRI bug account

Link to original bug (#105500)

Description

Created attachment 138094
dmesg

Hello there!

After connecting and enabling the 3rd monitor in D-Sub, the one with DP becames black. Most of the time I use 2 displays with (DVI-I and DP) without any problem. The desired layout is the following, however I even tried to use HDMI instead of DVI-I:
___ __ __
|DVI||DP||DS|
2 1 3

__ __ ____
|DS||DP||HDMI|
2 1 3

None of the options are working, however it's fine on Windows using the lastest - official beta - Crimson Edition 15.7.1.
The motherboard had an ASMedia ASM1445 DVI/HDMI bridge, so I couldn't use these outputs at the same time.

CPU: AMD A8-6500
GPU: AMD Radeon HD8570 (ATOMBIOSBK-AMD VER015.031.000.000.000000, 02/17/13,02:36:07)
MOBO: ASUS F2A85M-PRO (BIOS 6601)
OS: Arch Linux 4.13 AMD64
xf86-video-ati 1:18.0.0-1
xorg-server 1.19.6+13+gd0d1a694f-1

The logs/outputs were saved at 4.13, however it's not working with both the up-to-date Arch (4.15) and Xubuntu 18.04 beta.

Thank you

Attachment 138094, "dmesg":
dmesg