[Bug 73694] [hsw DP] Ubuntu 12.04 unable to use external monitor through edock

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=73694

--- Comment #30 from Jonathan McDowell <noodles at earth.li> ---
Testing with drm-intel-nightly (top of tree is
2ea23cd593ba60ead60e2f796fae675aa4475b1a) on a Dell E7240 (Haswell). Running up
to date Debian testing, xserver-xorg-video-intel version 2:2.21.15-2+b2.

Boot undocked, everything fine.
Plug into dock, attached monitor is not detected (tried both DVI ports on the
dock and the VGA port, xrandr shows nothing connected).

Boot docked, monitor (attached to DVI port 1) is detected, text KMS console
message display on both, once X starts built in laptop screen goes dark. Turns
out this is the backlight - if I hit the backlight keyboard keys it shows a
normal screen ok.
Unplug from dock, X restarts (back to gdm3 login).
Plug back into dock, dock attached monitor is not detected.

I'm not seeing anything that looks helpful in the dmesg (there's a pipe A
underrun error when booting docked) but I'll attach dmesg-no-dock and
dmesg-docked. I think it should be clear from when the USB devices change when
the laptop is being docked and undocked.

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