Video projector not detected anymore (under Xorg 1.18.4)

[Philippe Dosch]

Le 03/11/2016 à 17:05, Philippe Dosch a écrit :
> Le 03/11/2016 à 16:12, Łukasz Maśko a écrit :
>> Dnia czwartek, 3 listopada 2016 15:41:52 Philippe Dosch pisze:
>>> Hi Folks,
>>>
>>> I'm assistant professor and I teach with the same video projectors
>>> since years (with each of the last three kubuntu releases on my
>>> laptop). I have a strange trouble since my last kubuntu update (2
>>>
>>> weeks ago). Now I'm under kubuntu 16.10, with a 1.18.4 Xorg server:
>>
>> Hello!
>> I have exactly the same problem and it lies in the kernel itself,
>> probably in
>> i915 driver, not in X. The change was introuced in kernel 4.7.0, the
>> last of
>> the 4.6.x line (4.6.7) works fine. The changes deal with detection of
>> external
>> Display Port and as a result I get first an error like this:
>>
>> [drm:intel_dp_start_link_train [i915]] *ERROR* failed to update link
>> training
>
> Hi Dnia,
>
> I have the same message several times at boot time (also found in
> dmesg). But in my case, my troubles are related to the VGA port, not
> the display port.
>
>> at the kernel start (visible in dmesg). And then this output is not
>> recognized
>> anymore. I have filed a bug report
>> https://bugs.freedesktop.org/show_bug.cgi?id=97397
>
> I saw your post, but it is related to the display port and I don't
> know if the DP trouble makes some side effects with the VGA port.
>
>> Maybe you can confirm it or append yours so we make developers fix
>> this? I
>> have no idea how to fix this myself. I'm just keeping kernel 4.6.7 to
>> use when
>> I want to do my presentations.
>
> It's an idea, maybe I could downgrade to a 4.6.x kernel to see what
> happens.

I've installed and booted on a 4.6.3 kernel and it works! So, with a
4.8 kernel, impossible to connect an external video projector, but
possible with a 4.6.3.

I told you that your message was about a display port whereas mine was
about a VGA one. But, by looking closer, it is true that, even if my
projector is connected to the VGA port, it is logically seen as a DP
one:

phil at IUTNC-DOSCH testkern % xrandr 
                                   03-11-2016 17:39:19
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)

So, apparently, you're right with your analysis. I'm going to
contribute to your ticket.

If I have a good understanding, we have finally now to wait for a
kernel fix?

Thanks,
-- 
Philippe