[Bug 78162] New: [i7-4600U i915]: constant screen flickering after KMS which correlates with CPU load

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78162

          Priority: medium
            Bug ID: 78162
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: [i7-4600U i915]: constant screen flickering after KMS
                    which correlates with CPU load
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: konush at cern.ch
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

Created attachment 98309
  --> https://bugs.freedesktop.org/attachment.cgi?id=98309&action=edit
example of screen flickering

Dear developers,

Right after i915 sets native display resolution, boot screen starts to flicker.
Between flickers, text on the screen is sharp, colors are not distorted anyhow.
If there is no CPU activity, this flickering is almost absent, thereas the
amount of screen flickering is proportional to system load. For instance,
command "yes >/dev/null" leads to a lot of flickering (see examples attached).

The very same flickering happens if X is running. In any other aspect my system
runs normally.

The issue seems not to be related to MTRR register setup, but it may be related
to CPU/GPU transitions between various power states.

The system is Thinkpad t440s, i7-4600U, 1920x1080 touchscreen and additional
discrete NVidia GeForce GT 730M graphics card (which was disabled). Tested with
kernel-3.12.18 and kernel-3.15-rc2.

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