Here is bisect output:
636e2582658742b94e7620becce58f939996c961 is the first bad commit
commit 636e2582658742b94e7620becce58f939996c961
Author: Alex Deucher <alexander.deucher@amd.com>
Date:   Fri Jun 6 18:43:45 2014 -0400

    drm/radeon/dpm: add support for SVI2 voltage for SI

    Some newer boards use SVI2 for voltage control rather
    than GPIO.

    Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

:040000 040000 53449e086e151c24e90607b713c9bd416c658b55
72d3d0491cabfd6921a038565d8eeaca34726d5f M    drivers