After updating to kernel 4.9 I ended up with a blank screen after grub.
Booted back to 4.8 and checked logs and found a firmware file was showing as erroring and load not loading:
/lib/firmware/amdgpu/tonga_k_smc.bin
So I had to add that to firmware load files in the generic device drivers of the kernel and now all works.
It had a firmware file
/lib/firmware/amdgpu/tonga_smc.bin
before so the k one is new in 4.9.
