fixed in 4.6.0 rc5.

commit bfaddd9fc8ac048b99475f000dbef6f08297417f
Author: Alex Deucher <alexander.deucher@amd.com>
Date:   Mon Apr 18 11:19:19 2016 -0400

    Revert "drm/radeon: disable runtime pm on PX laptops without dGPU power
control"

    This reverts commit e64c952efb8e0c15ae82cec8e455ab4910690ef1.