I recently built a cheap gaming pc with the Ryzen 2200g processor with Vega 8 graphics. It worked well for many things, but for certain games (or totally randomly), the kernel would hang, requiring a REISUB restart.
The kernel log (/var/log/kern.log) would usually show erorrs such as:
[drm:amdgpu_job_timedout [amdgpu]] *ERROR* ring gfx timeout
A quick online search showed that this was a known problem, and I tried many of the suggested solutions – various kernel boot options, newer kernel versions (including compiling my own linux 5.2 kernel), and newer graphics drivers – with no success.
(For the record, I'm running Ubuntu 18.04, kernel version 4.18.0.24-generic. YMMV for other distros.)
The solution that worked for me was super simple. Installing the Radeon drivers directly from amd's website did the trick. Surprisingly, this didn't come up in my searches.
For Ubuntu, download the "Radeon™ Software for Linux® version 19.10 for Ubuntu
18.04.2", extract the archive, and then run ./amdgpu-pro-install -y. That's
it!