[SKL] Display resolution 3840x2160/60Hz do not work with docking station

Submitted by Jan Hoffmann

Assigned to Filip Kaczmarski

Link to original bug (#103786)

Description

Created attachment 135529
dmesg: Dock DP connector with converter

I'm using a T460 with the Thinkpad Ultra Dock (contains Synaptics DP MST hub) and a DP-HDMI converter (CAC-1070, based on PS176) to connect a 4K TV.

In this configuration the DP audio output is detected, but no audio can actually be heard. When connecting directly via HDMI or using the converter on the internal DP port of the laptop, audio works fine.

I have attached the dmesg output with drm.debug=0xe for the following test cases:

Dock DP connector with converter -> no audio
Internal DP connector with converter -> audio works
Dock HDMI connector -> audio works
Internal HDMI connector -> audio works

Attachment 135529, "dmesg: Dock DP connector with converter":
dmesg-dp-dock.txt