I'm running ubuntu 18.04.3 LTS kernel 5.0.0-25-generic, I use to have 18.50-756341 which works well with my Radeon VII and my rx 550.
I've removed drv 18.50-756341, then I installed 19.30-838629.
When running clinfo, it only detects the 'PAL' platform of the radeon VII, not the 'legacy' one for RX 550, same for RX 580.
I've also tried with 19.30-855429 same issue.
It seems OpenCL support for Polaris is missing in this driver.
Did you get it working by now?
Just wondering if you tried the explicit option of amdgpu-install to select legacy OCL drivers. Or, did you use that option, which is why you thought it was weird that it didn't detect?