[Bug 85670] [hsw DP] Haswell Iris 5100 DisplayPort stops working when USB device is connected

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=85670

--- Comment #6 from Jani Nikula <jani.nikula at intel.com> ---
(In reply to Andrzej Pronobis from comment #0)
> however, if the external monitor is
> configured after the USB device is plugged in, then the following backtrace
> appears in dmesg:
> 
> [   57.685383] ------------[ cut here ]------------
> [   57.685396] WARNING: CPU: 0 PID: 1879 at
> /build/buildd/linux-3.16.0/drivers/gpu/drm/i915/intel_dp.c:3122
> intel_dp_link_down+0x1a9/0x230 [i915]()
> [   57.685397] Modules linked in: cdc_ether usbnet r8152 mii pci_stub
...
> [   57.688050] [drm:intel_dp_complete_link_train] *ERROR* failed to train
> DP, aborting

Please attach dmesg with drm.debug=14 module parameter set, from boot to this
problem, i.e. plug a problematic USB3 device in first, then the DP cable.

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