[Bug 92591] New: [SKL]=?UTF-8?Q?=C2=A0Bogus=20values=20reported=20?=(randomly) for GPU frequency requests in sysfs

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=92591

            Bug ID: 92591
           Summary: [SKL] Bogus values reported (randomly) for GPU
                    frequency requests in sysfs
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: mika.kuoppala at intel.com
          Reporter: eero.t.tamminen at intel.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org,
                    valtteri.rantala at intel.com
     i915 platform: SKL
     i915 features: power/Other

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.

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