Comment 18 for bug 1568429

I have the same problem after upgrading to 16.04 from 14.04.
I am using a Kaveri APU, that is supposed to work with both "radeon" and "amdgpu" drivers.
The "radeon" driver doesn't work: after the very initial steps of the bootstrap, the screen goes black, although a may access the system via SSH.
Setting "nomodeset" prevents the "radeon" driver to start, reverting back to basic driver.
However, the new "amdgpu" driver seems working fine.
I managed to fix the issue in the following way:
1. blacklist "radeon", by creating a new file /etc/modprobe.d/blacklist-radeon.conf having a single line "blacklist radeon";
2. force "amdgpu", by appending to /etc/modules the line "amdgpu";
3. setting the screen resolution in grub, by uncomment the line GRUB_GFXMODE, e.g. "GRUB_GFXMODE=1280x1024";
4. create a new file /etc/X11/xorg.conf, having a block
     Section "Device"
       Identifier "VideoCard"
       DriveR "amdgpu"
     EndSection
5. update initramfs, via "update-initramfs -u -k all" with sudo;
6. update grub configuration, via "update-grub" with sudo.
Maybe other user having a GCN-enabled AMD video card may fix the issue in the same way.