I was excited to update to Crimson 16.12.1 once I heard that WattMan was going to be available on older GCN GPUs.
Before upgrading, I had my MSI Gaming R9 390 undervolted by 100mV to achieve my desired power draw and thermals; however, following the update to 16.12.1, booting with my undervolt via MSI Afterburner caused a system crash, and would not boot without the voltage being returned to normal. I decided to try and perform my undervolt through the WattMan settings, though I discovered that I Power states 2-7 would not change, regardless of the voltage input.
I hope this issue can be solved, because I have been loving the incredible efficiency that can be achieved with my custom settings.
Until the issue is resolved, I will remain on 16.11.4, which is a shame, because I am genuinely excited about many of the features that it brings.