Din't you forget to add 'amdgpu.vm_fragment_size=9'? Without that module option the hashrate will be the same.

As for me, rocm kernel works as expected. Except it does not downvolt cards. I tried SMOS with original kernel and rocm. With original it can decrease power consumption, but has low hashrate. With rocm kernel the hashrate is higher, but DPM state changes do nothing, consumption is always high.