Looking at the info i supplied in http://www.linuxquestions.org/questions/slackware-14/current-14-2-and-dri-3-and-dri_prime-ain't-working-4175578108/ It looks like it's related to 94874 only kernel versions differ. https://bugs.freedesktop.org/show_bug.cgi?id=94874 If the commit is reverted from the 4.4.y and 4.5.y this could be marked as solved.