[Bug 91476] New: Fedora 23 kernels lock up with Lenovo ThinkPad T440s in monitor connected Ultradock

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91476

            Bug ID: 91476
           Summary: Fedora 23 kernels lock up with Lenovo ThinkPad T440s
                    in monitor connected Ultradock
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: tcallawa at redhat.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

I'm using a Lenovo ThinkPad T440s with the latest BIOS installed (and the
latest firmware applied to the UltraDock). When I put the laptop in the
Ultradock with a monitor connected (DVI), the kernel starts to boot, but
freezes hard very early in the process. No errors are shown, even with
drm.debug=6. If I boot without the laptop in the dock, it boots up fine. If I
put the booted laptop in the dock, the system freezes and the laptop panel goes
dark. If I then undock the laptop, it resumes normal operation.

If I disconnect the external monitor from the UltraDock, then boot with the
laptop docked, it works properly. 

I had this issue back in Fedora 20, until I updated the firmware on the
UltraDock. This all was working fine from then. through Fedora 21 and 22, but
stopped working with Fedora 23 (in fact, if I boot into the rescue kernel from
22, it works again). Kernels where I see this failure are:

kernel-4.2.0-0.rc2.git1.1.fc23.x86_64
kernel-4.2.0-0.rc3.git2.1.fc23.x86_64
kernel-4.2.0-0.rc3.git4.1.fc23.x86_64

Let me know what I can do to help debug this issue, it's really annoying.

Internal GPU:
0:02.0 VGA compatible controller: Intel Corporation Haswell-ULT Integrated
Graphics Controller (rev 0b)

External monitor is an Acer AL2223W.

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