Just adding a data point here, I've got an MSI R9 390 running =
on Ubuntu 18.04
on 4.15.0-10-generic - I haven't had any stability issues, but I have had
maddening screen flickering/corruption.

I'm running dual 2560x1440 monitors off the card, which forces the memory c=
lock
to 1500MHz. However, when the GPU clock is at the 300MHz level, I get
horrendous artifacting any time an accelerated portion of the screen is dra=
wn.
I can easily reproduce the issue by mousing over certain KDE widgets which =
are
acclerated. Interestingly, running glxgears doesn't cause the issue.

* Setting power_dpm_force_performance_level -> high fixes it (but runs t=
he
clock up to its max, obviously)
* Setting power_dpm_force_performance_level -> manual and then `echo 123=
4567 >
pp_dpm_sclk` fixes it, with the GPU clock fixed to 500MHz.

I've been up and down this issue with both radeon and amdgpu drivers; neith=
er
seems to make a difference.

# lspci -nnk | grep -iA2 vga
06:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc.
[AMD/ATI] Hawaii PRO [Radeon R9 290/390] [1002:67b1] (rev 80)
        Subsystem: Micro-Star International Co., Ltd. [MSI] Hawaii PRO [Rad=
eon
R9 290/390] [1462:2015]
        Kernel driver in use: amdgpu

# cat vbios_version
MS-V30823-F6

(Interestingly, this BIOS is newer than anything on techpowerup. I was hopi=
ng a
BIOS flash would fix it, but I can't find anything newer)

I'll attach dmesg and Xorg logs as well. If I can provide extra data points,
I'd like to help.