Radeon problem: GUI unresponsive

Linux Mint
1

I was using LibreOffice, and suddenly it became very slow and while the mouse could move, the graphical interface stopped responding to its clicking. I Ctrl-Alt-F1’d over to the console, opened /var/log/syslog and found this (the part from the ‘WB enabled’ line onwards loops):

Nov 20 14:58:41 ********** kernel: [341019.367849] [drm] probing gen 2 caps for device 1022:157c = 733c43/e
Nov 20 14:58:41 ********** kernel: [341019.367854] [drm] enabling PCIE gen 3 link speeds, disable with radeon.pcie_gen2=0
Nov 20 14:58:42 ********** kernel: [341020.747123] [drm] PCIE GART of 2048M enabled (table at 0x0000000000040000).
…
Nov 20 15:09:03 ********** kernel: [341641.928875] radeon 0000:01:00.0: WB enabled
Nov 20 15:09:03 ********** kernel: [341641.928879] radeon 0000:01:00.0: fence driver on ring 0 use gpu addr 0x0000000080000c00 and cpu addr 0x00000000f82a8c6f
Nov 20 15:09:03 ********** kernel: [341641.928881] radeon 0000:01:00.0: fence driver on ring 1 use gpu addr 0x0000000080000c04 and cpu addr 0x000000001f4d0590
Nov 20 15:09:03 ********** kernel: [341641.928883] radeon 0000:01:00.0: fence driver on ring 2 use gpu addr 0x0000000080000c08 and cpu addr 0x000000002fa3e9d2
Nov 20 15:09:03 ********** kernel: [341641.928885] radeon 0000:01:00.0: fence driver on ring 3 use gpu addr 0x0000000080000c0c and cpu addr 0x0000000036fe76af
Nov 20 15:09:03 ********** kernel: [341641.928886] radeon 0000:01:00.0: fence driver on ring 4 use gpu addr 0x0000000080000c10 and cpu addr 0x000000002041b940
Nov 20 15:09:03 ********** kernel: [341642.240716] [drm] ring test on 0 succeeded in 1 usecs
Nov 20 15:09:03 ********** kernel: [341642.240724] [drm] ring test on 1 succeeded in 1 usecs
Nov 20 15:09:03 ********** kernel: [341642.240730] [drm] ring test on 2 succeeded in 1 usecs
Nov 20 15:09:03 ********** kernel: [341642.240740] [drm] ring test on 3 succeeded in 3 usecs
Nov 20 15:09:03 ********** kernel: [341642.240747] [drm] ring test on 4 succeeded in 3 usecs
Nov 20 15:09:03 ********** kernel: [341642.240792] [drm] ib test on ring 0 succeeded in 0 usecs
Nov 20 15:09:03 ********** kernel: [341642.240822] [drm] ib test on ring 1 succeeded in 0 usecs
Nov 20 15:09:03 ********** kernel: [341642.240852] [drm] ib test on ring 2 succeeded in 0 usecs
Nov 20 15:09:03 ********** kernel: [341642.240869] [drm] ib test on ring 3 succeeded in 0 usecs
Nov 20 15:09:03 ********** kernel: [341642.240882] [drm] ib test on ring 4 succeeded in 0 usecs

What cure is there for it? I find two kinds of advice on the Web: some suggest installing an AMD driver and some replacing the Cinnamon desktop with Mate or something.
Specifications:

System:
  Kernel: 4.15.0-70-generic x86_64 bits: 64 
  Desktop: Cinnamon 4.2.4 Distro: Linux Mint 19.2 Tina
Graphics:
  Device-1: AMD Stoney [Radeon R2/R3/R4/R5 Graphics] driver: amdgpu 
  v: kernel 
  Device-2: AMD Sun LE [Radeon HD 8550M / R5 M230] driver: radeon v: kernel 
  Display: x11 server: X.Org 1.19.6 driver: ati,radeon 
  unloaded: amdgpu,fbdev,modesetting,vesa resolution: 1366x768~60Hz 
  OpenGL: renderer: AMD STONEY (DRM 3.23.0 4.15.0-70-generic LLVM 8.0.0) 
  v: 4.5 Mesa 19.0.8
2

that was more than i could find. i came across a few different bug reports, but never any fix mentioned or even hinted at.

i did find this link which is dated (only addresses issues up to ubuntu 16.04), but suggested the following command to see if there are any boot messages/errors: dmesg | egrep 'drm|radeon'

perhaps that will give some other info to try and look into.