[Assist] Radeon graphics problems after updating from Linux-libre 4.5.4 to 4.6.1

[D.]

Hello,

Ever since updating Linux-libre from 4.5.4 to 4.6.1 in June, video has
started freezing at boot. I can log in and operate the computer, but
video is frozen at finished fsck.

The computer experiencing problems has two graphics processors: ATI
Mobility Radeon HD 4250 and AMD Radeon HD 6650M. Graphics used to work
fine before.

The problem can be temporarily fixed by disabling kernel mode setting in
GRUB. However, Redshift doesn't work any more and performance is poor.

I have xf86-video-ati, xf86-video-fbdev and xf86-video-vesa installed.

Also the current Linux-libre version installed is the latest (4.6.5) but
the problem that came with 4.6.1 persists.

Any suggestions on fixing or working around this problem will be
appreciated.

Thanks,
D.