[Bug 116361] New: Blank screen after KMS loads on ThinkPad T430 with dual monitors

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=116361

            Bug ID: 116361
           Summary: Blank screen after KMS loads on ThinkPad T430 with
                    dual monitors
           Product: Drivers
           Version: 2.5
    Kernel Version: 4.4.5-1-ARCH
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - Intel)
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: virtajus at gmail.com
                CC: intel-gfx-bugs at lists.freedesktop.org
        Regression: No

This particular machine uses Intel i5-3320M processor. It does not have an
external GPU. The machine supports two active outputs. In the bios there is an
option to change output display during boot. I will describe the behaviour of
booting verbosely to avoid confusion. Depending on the choice, and with two
external monitors attached, the following happens:


 Laptop display as boot display, laptop lid open:
Boot loader shows up on the laptop display. External displays are off. After
KMS loads, laptop display goes blank but the backlight stays on. External
displays stay off.

 Laptop display as boot display, laptop lid closed:
Boot loader shows up on the first external display. Second external display is
off. After KMS loads, first display goes blank but the backlight stays on.
Second display stays off. Presumably, laptop display is off at all times.

 First external display as boot display, laptop lid open:
Boot loader shows up on the first external display. Other displays are off.
After KMS loads, first display goes blank but the backlight stays on. Other
displays stay off.

 First external monitor as boot display, laptop lid closed:
Boot loader shows up on the first external display. Second external display is
off. After KMS loads, first display goes blank but the backlight stays on.
Second display stays off. Presumably, laptop display is off at all times.


Setting the boot display to second external monitor behaves similarly as the
last two cases, but with first and second monitor reversed.

Currently I'm using a dock to connect the two external monitors via DP and DVI
- however, connecting them straight into the DP and VGA ports of the laptop has
the same effect.

The machine is responsive after KMS, since I can log in and start X by memory,
after which I have output as expected.

As a temporary fix I've added the kernel parameter "video=LVDS-1:d" which
completely disables the internal laptop display during boot. This enables
output on the external monitors after KMS loads. Downside of this is that I
cannot detach external displays and continue working on the internal monitor
without rebooting. Also, with only one external monitor attached, everything
works as expected.

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