[Bug 93208] New: Blank screen and dmesg errors with two external monitors

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93208

            Bug ID: 93208
           Summary: Blank screen and dmesg errors with two external
                    monitors
           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: bartolinidb at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

I am on a Thinkpad T450, if I connect a single external monitor, either via
miniDP or VGA, everything works fine.
If I connect both monitors, all output disappears and the only way to restore
is to go back to a text console and restart the display manager.

In dmesg, I get a lot of these messages:

[drm:gen8_irq_handler [i915]] *ERROR* The master control interrupt lied (SDE)!

I found other bugs that report the same error message, but they seem to be
triggered by different conditions.

The two monitor used to work on a previous kernel (I'm not sure what version,
probably before 4.2).

Additional information follows:

$ uname -a
Linux davide 4.4.0-040400rc3-generic #201511300321 SMP Mon Nov 30 03:23:36 UTC
2015 x86_64 x86_64 x86_64 GNU/Linux

$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Broadwell-U Integrated
Graphics (rev 09)

$ lsmod | grep i915
i915                 1204224  9
i2c_algo_bit           16384  1 i915
drm_kms_helper        135168  1 i915
drm                   360448  10 i915,drm_kms_helper
video                  40960  2 i915,thinkpad_acpi

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