[Bug 87327] New: Hang when reconnecting to an external monitor using a docked Lenovo T540p

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87327

            Bug ID: 87327
           Summary: Hang when reconnecting to an external monitor using a
                    docked Lenovo T540p
           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: tytso at mit.edu
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 110862
  --> https://bugs.freedesktop.org/attachment.cgi?id=110862&action=edit
Dmesg after a resume

I've been having severe problems with docking with my Lenovo T540p using an
external dock (which uses a MST hub in the dock).    The system will often
hang, crash, or simply not recognize the external monitor until I restart the X
server.   I've documented a number of these problems on the dri-devel mailing
list for example, with the subject line "Re: WARNING:
 /usr/projects/linux/linux/drivers/gpu/drm/i915/intel_pm.c:6585
 intel_display_power_put+0x4b/0x116 [i915]()".   This is a new one.


This morning, I was docked and using a Dell 30" monitor.  I
reconfigured the X server to stop sending video to the external
monitor, suspended the laptop, and after it was suspended undocked it
and took it to work.  Then I docked it at work, where it was connected
to a powered off Dell 24" monitor, the system competely hung.  One of the
things that I've learned will unwedge the system after it hangs after unsuspend
is to eject the laptop from the dock, and wait.   Eventually the system did
unwedge, and then I redocked it.  Afterwards, I found the following in dmesg
and in /sys/class/drm/card0/error.  (See attached.)

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