Bug 92591

USE-CASE:

1. Start sampling kernel's GPU frequency request values:
   while true; do head /sys/class/drm/card0/gt_cur_freq_mhz; sleep 1; done

2. Run heavy GPU benchmark like Unigine Heaven, Lightsmark 2008, GfxBench 3.x Manhattan.


EXPECTED OUTCOME:

* reported kernel GPU freq request is within min and max GPU frequencies


ACTUAL OUTCOME:

* On SKL-Y machine with supported GPU frequencies in 350-800 Mhz range, gt_cur_freq_mhz sometimes reports values within this range, sometimes obviously bogus higher ones (about 4x higher).  

* On SKL-i5 machine with supported GPU frequencies in 350-1150 Mhz range, gt_cur_freq_mhz sometimes reports values within this range, sometimes obviously bogus higher ones (about 3x higher).  


This issue has been visible in drm-intel-nightly kernels since we started testing SKL devices.


Note: CAGF (gt_act_freq_mhz) value asked from GPU is always within the correct MHz range.  (Sometimes it's not divisable with 50, like the requests, but that's probably not an issue.)

Assigning to Mika as he said that that he might take a look at this at some point.