Due to a regression introduced in the 4.12.3 kernel, resume from suspend doesn't work for amdgpu on AMD RX480 boards (which I can confirm) (also reportedly RX470 doesn't work either). There is a bug report about that in archlinux https://bbs.archlinux.org/viewtopic.php?id=228922 and here https://bugzilla.kernel.org/show_bug.cgi?id=196615 and the commit which introduced the bug https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-4.12.y&id=2dc1889ebf8501b0edf125e89a30e1cf3744a2a7 Alex Deucher who made the commit has provided a patch (which is basically deleting one line in amdgpu_cgs.c) which reverts the patch that introduced the bug. Could this be added to the gentoo patchset for at least the stable 4.12.5 kernel? Furthermore, on my machine the bug introduced some random display flickering every few seconds.
I'm sorry, the regression was introduced in the linux kernel 4.12.4.
