To potentially save someone from sinking tons of time into this when it might be doomed to fail: if you are planning on using a Polaris GPU, ROCm will not work on POWER currently due to the lack of PCIE atomics. According to
this issue, Vega+ might be fine without them. I double checked if the lack of PCIE atomics was still an issue in 2023, and I would sadly say so:
[ 14.145631] amdgpu 0000:01:00.0: amdgpu: PCIE atomic ops is not supported
[ 14.811332] kfd kfd: amdgpu: skipped device 1002:67c4, PCI rejects atomics 730<0