[Bug 97397] Kernel 4.7.x does nor initialize external DisplayPort in Dell E7250 making it unusable

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97397

--- Comment #4 from Philippe Dosch <loirotte at gmail.com> ---
Hi,

It seems that I meet the same bug after having upgraded from ubuntu
16.04 to ubuntu 16.10. I'm now with a 4.8.0 kernel. Since the upgrade,
I'm unable to connect a video projector on my VGA port (whereas it has
perfectly worked with the two former releases). Strangely, if I
connect an external monitor with the same resolution than my laptop
(1920x1080), the monitor is detected and works. After having met
Lukasz on the Xorg ML, I've tried to boot on a 4.6.3 kernel and I'm
now able to make the video projector works.

Details on my configuration
===========================

Laptop HP EliteBook 840 with a i915 graphics card using kubuntu 16.10,
and a video projector connected to the VGA port.

1) Kernel 4.8.0
   ------------

phil at IUTNC-DOSCH i915 % uname -a
Linux IUTNC-DOSCH 4.8.0-26-generic #28-Ubuntu SMP Tue Oct 18 14:39:52 UTC 2016
x86_64 x86_64 x86_64 GNU/Linux

When I boot, the message "[drm:intel_dp_start_link_train [i915]]
*ERROR* failed to update link training" appears 3 times in dmesg.

phil at IUTNC-DOSCH i915 % xrandr

Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
eDP-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y
axis) 309mm x 173mm
   1920x1080     60.05*+  59.93  
   1680x1050     59.95    59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1280x1024     60.02  
   1440x900      59.89  
   1280x960      60.00  
   1360x768      59.80    59.96  
   1152x864      60.00  
   1024x768      60.04    60.00  
   960x720       60.00  
   928x696       60.05  
   896x672       60.01  
   960x600       60.00  
   960x540       59.99  
   800x600       60.00    60.32    56.25  
   840x525       60.01    59.88  
   800x512       60.17  
   700x525       59.98  
   640x512       60.02  
   720x450       59.89  
   640x480       60.00    59.94  
   680x384       59.80    59.96  
   576x432       60.06  
   512x384       60.00  
   400x300       60.32    56.34  
   320x240       60.05  
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
HDMI-2 disconnected (normal left inverted right x axis y axis)

2) Kernel 4.6.3
   ------------

phil at IUTNC-DOSCH ~ % uname -a
Linux IUTNC-DOSCH 4.6.3-040603-generic #201606241434 SMP Fri Jun 24 18:36:33
UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

When I boot, there is none message as the one above (so no more error
message about the i915 card). Even if the video projector is
physically connected to the VGA port, it seems it is logically seen as
a DP one:

phil at IUTNC-DOSCH testkern % xrandr
Screen 0: minimum 320 x 200, current 1920 x 1848, maximum 8192 x 8192
eDP-1 connected primary 1920x1080+0+768 (normal left inverted right x axis y
axis) 309mm x 173mm
   1920x1080     60.05*+  59.93
   1680x1050     59.95    59.88
   1600x1024     60.17
   1400x1050     59.98
   1280x1024     60.02
   1440x900      59.89
   1280x960      60.00
   1360x768      59.80    59.96
   1152x864      60.00
   1024x768      60.04    60.00
   960x720       60.00
   928x696       60.05
   896x672       60.01
   960x600       60.00
   960x540       59.99
   800x600       60.00    60.32    56.25
   840x525       60.01    59.88
   800x512       60.17
   700x525       59.98
   640x512       60.02
   720x450       59.89
   640x480       60.00    59.94
   680x384       59.80    59.96
   576x432       60.06
   512x384       60.00
   400x300       60.32    56.34
   320x240       60.05
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 connected 1024x768+424+0 (normal left inverted right x axis y axis) 0mm x
0mm
   1024x768      60.00*
   800x600       60.32    56.25
   848x480       60.00
   640x480       59.94
HDMI-2 disconnected (normal left inverted right x axis y axis)

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