[Bug 94337] New: Linux 4.5 regression: FIFO underruns on Skylake

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94337

            Bug ID: 94337
           Summary: Linux 4.5 regression: FIFO underruns on Skylake
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: luto at mit.edu
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

See previous discussion here:
https://lists.freedesktop.org/archives/intel-gfx/2016-February/087710.html

On my Skylake laptop (Dell XPS 13 9350), I see relatively frequent FIFO
underruns.  This only happens after suspend/resume -- I haven't seem them
before the first suspend after a reboot.

My best guess is that this is the same issue as bug 93945 but that the fix for
that bug didn't work on Skylake.  However, I *do* see underruns while the
cursor is visible, but I don't seem to see them unless I've stopped interacting
with the machine for a second or two.

The problem is still present in 4.5-rc6.  I'm using Fedora 23.

I can't dump VBIOS because "i915 0000:00:02.0: Invalid PCI ROM header
signature: expecting 0xaa55, got 0xffff".  I'll keep poking PCI maintainers
about that.  intel_reg_dumper output is in the mailing list thread.

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