[Bug 92003] New: SKL: Display underruns

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=92003

            Bug ID: 92003
           Summary: SKL: Display underruns
           Product: DRI
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: dan at reactivated.net
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Every now and then, the display momentarily blinks to black, and the following
message appears in the log:

[drm:intel_cpu_fifo_underrun_irq_handler] *ERROR* CPU pipe A FIFO underrun

Reproduced on Linux 4.2 and 4.3-rc1, on a new Skylake laptop with quad-core i5
6200U. The laptop seems rather beefy so I have trouble believing this is a
general RAM bandwidth issue.

This is using just the internal laptop display, 1920x1080. Sometimes the
problem happens a lot, and sometimes it takes a while. However, I find that I
can't complete a grand prix in SuperTuxKart (about 20 mins gameplay) without
this happening at least once (usually more times).

I can't reproduce on intel-drm-nightly, however SuperTuxKart gameplay is not as
smooth there, every few minutes the display hangs for approximately 1 second,
with no messages in the log.

00:02.0 VGA compatible controller: Intel Corporation Device 1916 (rev 07)
(prog-if 00 [VGA controller])
    Subsystem: ASUSTeK Computer Inc. Device 1c3d
    Flags: bus master, fast devsel, latency 0, IRQ 123
    Memory at de000000 (64-bit, non-prefetchable) [size=16M]
    Memory at c0000000 (64-bit, prefetchable) [size=256M]
    I/O ports at f000 [size=64]
    Expansion ROM at <unassigned> [disabled]
    Capabilities: [40] Vendor Specific Information: Len=0c <?>
    Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
    Capabilities: [ac] MSI: Enable+ Count=1/1 Maskable- 64bit-
    Capabilities: [d0] Power Management version 2
    Capabilities: [100] #1b
    Capabilities: [200] Address Translation Service (ATS)
    Capabilities: [300] #13
    Kernel driver in use: i915

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