Black second screen after 18.04 update

Question

After update to 18.04 from 17.10, my second monitor seems to be detected (though weirdly as " Samsung Electric Company 19" " when it actually is Samsung SyncMaster 940N) but is black. It is set to join displays and I can blindly manipulate stuff on the second display desktop space.

I have vanilla Gnome installed though switching to Ubuntu styled Gnome changes nothing. Forcing no wayland also doesn't seem to do anything.

What can be the problem?

Edit:

Result of lspci -nnk | grep -A3 -Fe '[0300]':

01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Tonga XT / Amethyst XT [Radeon R9 380X / R9 M295X] [1002:6938] (rev f1)
Subsystem: Gigabyte Technology Co., Ltd Radeon R9 380X [1458:22c8]
Kernel driver in use: amdgpu
Kernel modules: amdgpu

Result of xrandr using single display mode:

Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384
DisplayPort-0 disconnected (normal left inverted right x axis y axis)
HDMI-A-0 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 598mm x 336mm
   1920x1080     60.00*+  50.00    59.94  
   1680x1050     59.88  
   1600x900      60.00  
   1280x1024     60.02  
   1440x900      60.00  
   1280x960      60.00  
   1280x800      59.91  
   1280x720      60.00    50.00    59.94  
   1024x768      60.00  
   1024x576      59.97  
   800x600       60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       60.00    59.94  
DVI-D-0 disconnected (normal left inverted right x axis y axis)
DVI-D-1 connected (normal left inverted right x axis y axis)
   1280x1024     60.02 +  75.02  
   1280x960      60.00  
   1280x800      60.02  
   1152x864      75.00  
   1280x720      60.02  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   640x480       75.00    72.81    66.67    59.94  
   720x400       70.08 

Result of xrandr using mirror display mode:

Screen 0: minimum 320 x 200, current 1280 x 1024, maximum 16384 x 16384
DisplayPort-0 disconnected (normal left inverted right x axis y axis)
HDMI-A-0 connected primary 1280x1024+0+0 (normal left inverted right x 
axis y axis) 598mm x 336mm
   1920x1080     60.00 +  50.00    59.94  
   1680x1050     59.88  
   1600x900      60.00  
   1280x1024     60.02* 
   1440x900      60.00  
   1280x960      60.00  
   1280x800      59.91  
   1280x720      60.00    50.00    59.94  
   1024x768      60.00  
   1024x576      59.97  
   800x600       60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       60.00    59.94  
DVI-D-0 disconnected (normal left inverted right x axis y axis)
DVI-D-1 connected 1280x1024+0+0 (normal left inverted right x axis y 
axis) 376mm x 301mm
   1280x1024     60.02*+  75.02  
   1280x960      60.00  
   1280x800      60.02  
   1152x864      75.00  
   1280x720      60.02  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   640x480       75.00    72.81    66.67    59.94  
   720x400       70.08  

Edit:

I poked around, reinstalled gnome, made sure I have latest open amd drivers: https://launchpad.net/~oibaf/+archive/ubuntu/graphics-drivers, searched for the same problems but couldn't find any. It continues to work flawlessly on Win10. What 17.10->18.04 update could've done to make secondary screen black?

Edit:

Tried Live USB and live environment has the same problem, so it seems like there is something incompatible with 18.04.

Solution

I am seeing this advice ... to quote "Try adding amdgpu.dc=0 to the kernel command line at boot"

Dual Monitors on 18.04 with Radeon RX 580 GPU

sudo vi /etc/default/grub

old

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" 

new

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash amdgpu.dc=0"

save then issue

sudo update-grub

then reboot

Comments

[Virgileo]

Edited, and I've set the "Single Display" mode by the way.

[WinEunuuchs2Unix]

If extended desktop isn't working properly try mirror mode first until all the glitches are worked out.

[Virgileo]

Ok, added the output for mirrored displays but on the second display still nothing is shown.

[Virgileo]

Where have you been, the savior? Ok so before I've seen your answer I went ahead and checked if Live USB would work. It didn't so I tried Fedora USB and it worked so I figured the problem somewhere in Ubuntu. I then installed fedora and it worked. But then after the first system update the same problem have risen. But this solution did work: I changed GRUB_CMDLINE_LINUX adding amdgpu.dc=0 and ran sudo grub2-mkconfig -o /boot/grub2/grub.cfg (as Fedora doesn't have update-grub). And after the reboot second monitor worked again.