https://bugs.freedesktop.org/show_bug.cgi?id=91278
--- Comment #47 from Andy Furniss adf.lists@gmail.com --- Seems like you are using an old kernel - though what I call old may be current for what's released.
The hanging for me stopped with 4.4, but 4.3 is release.
If you are using 4.3 maybe booting with the option -
amdgpu.enable_scheduler=1
will help.
If you are used to compiling your own kernels then using one from -
http://cgit.freedesktop.org/~agd5f/linux/
like drm-next-4.4 should be stable.
Or if you want to test/use the new powerplay try amdgpu-powerplay