[PATCH][SRU][Bionic][8086:3e92] display becomes blank after S3

[AceLan Kao]

BugLink: https://bugs.launchpad.net/bugs/1763271

[Impact]
The display becomes black after S3 with the following error messages.

dmesg:
[ 60.546305] [drm:intel_dp_start_link_train [i915]] Link Training failed at link rate = 540000, lane count = 4

Xorg.0.log:
[ 60.748] (EE) modeset(0): failed to set mode: Invalid argument
[ 60.748] (WW) modeset(0): hotplug event: connector 48's link-state is BAD, tried resetting the current mode. You may be left with a black screen if this fails...

[Fix]
Looks like link training fallback fails sometimes with eDP, we need this commit to fix the issue.

commit a306343bcd7df89d9d45a601929e26866e7b7a81 (refs/bisect/bad)
Author: Manasi Navare <manasi.d.navare at intel.com>
Date: Thu Oct 12 12:13:38 2017 -0700

    drm/i915/edp: Do not do link training fallback or prune modes on EDP

[Regression Potential]
Should be low. The behavior only changes when DP is eDP, it does nothing if DP is eDP. Should be fine to not do link training fallback and not emit Hotplug Uevent to userspace to start modeset, since its eDP, the display is fixed.

Manasi Navare (1):
  drm/i915/edp: Do not do link training fallback or prune modes on EDP

 drivers/gpu/drm/i915/intel_dp_link_training.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

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2.7.4