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

Submitted by Balázs Vinarz

Assigned to Default DRI bug account

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