Created attachment 130835 [details]
dmesg log

First of all, this is the first bug reported by me, so I apologize in advance
if I assigned it to a wrong category. I have a monitor, a DisplayPort cable and
two notebooks. When the monitor is connected to the first notebook (Lenovo
T440), everything works fine, so the cable seems is working fine. Now, when the
monitor is connected to the second notebook, it shows "no signal is detected"
and switches into sleep mode. Here is what dmesg outputs (I will attach the
complete dmesg log):

[   12.064503] [drm:radeon_dp_link_train [radeon]] *ERROR* displayport link
status failed
[   12.064517] [drm:radeon_dp_link_train [radeon]] *ERROR* clock recovery
failed

Of course, after logging into the X session, the monitor remains black,
although Xorg does not report any errors in log:

$ grep -n EE /var/log/Xorg.0.log
16:     (WW) warning, (EE) error, (NI) not implemented, (??) unknown.

System:

Linux msi_gx70 4.10.9-gentoo #2 SMP Thu Apr 13 21:30:04 CEST 2017 x86_64 AMD
A10-5750M APU with Radeon(tm) HD Graphics AuthenticAMD GNU/Linux