[Bug 109806] New: [REGRESSION] X fails to start properly in 4.20.13

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109806

            Bug ID: 109806
           Summary: [REGRESSION] X fails to start properly in 4.20.13
           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: tibbs at math.uh.edu
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

After updating from 4.20.12 to 4.20.13, I found that a couple of my machines
failed to start X properly.  Things work when booting back to 4.20.12 with no
other changes made to the system.  I note that there are a few i915-related
patches which are new to 4.20.13.  I will be away for a few days but next week
I'll try reverting some of them.

I'm running 4.20.13 on well over a hundred other hosts and haven't seen any
complaints about them yet, though I haven't personally checked them all either.
 So what's special about these two hosts?

Both machines have i5-4670 CPUs and are running with the integrated graphics,
which I guess is Haswell. lspci says:

00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 
v3/4th Gen Core Processor Integrated Graphics Controller (rev 06)

Certainly not a Xeon but I guess that's a generic PCI ID.

Both machines have two of a particular type of cheap monitor, and I think
that's why these two machines are special as none of my other machines have
those monitors.  Looking at the EDID info, all of the displays have the same
manufacturer, model, year/week of manufacture and serial number ("0").  I've
had a few problems in the past with desktop environments trying to be smart
about the monitor layout and being confused by the monitors being essentially
identical.

I wonder if it's possible that this new-in-4.20.13 patch is related?
    drm/i915/fbdev: Actually configure untiled displays
I guess that would be the first thing I'd try to revert.

In any case, I have no other machines that have two of those particular
annoying monitors.

I'll attach dmesg from each kernel when booted with drm.debug=0x06, as well as
the Xorg logs.

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