https://bugzilla.kernel.org/show_bug.cgi?id=76861
--- Comment #1 from Christian König deathsimple@vodafone.de --- Created attachment 137371 --> https://bugzilla.kernel.org/attachment.cgi?id=137371&action=edit Possible fix
Might be caused by the recent PLL changes. Does the attached patch helps?
Also please provide dmesg output generated with drm.debug=0xE on the kernel commandline.