Created attachment 123520 [details]
entire dmesg from the boot #1

I have HP zbook 14 and using Debian testing/unstable.  External monitor is
connected to docking station serving two DP connections.  To make those visible
to xrandr I do

xrandr --setprovideroffloadsink 1 0
xrandr --setprovideroutputsource 1 0

where 0 corresponds to Intel, 1 to Radeon/OLAND (name changed when upgraded).
Setup was working with stock debian packages (kernel was 4.4.2-3) for awhile
but there was an issue that display didn't refresh correctly and often I had
blank patches and had to go to gnome overview and back to re-render.  So I have
decided to upgrade to a current state of testing + some unstable.  Currently
have xserver-xorg-core 2:1.18.3-1  xserver-xorg-video-ati 1:7.7.0-1  and kernel
4.5.1-1 .  Unfortunately I can't "turn on" the external display connected to
the docking station -- screen blinks and comes back to display on the laptop,
xrandr reports xrandr: Configure crtc 4 failed   and agd5f on IRC looking at
http://www.onerussian.com/tmp/dmesg-20160506-1.txt (attached to this report as
well) summarized as "link training failed on the display"