[Bug 98140] New: External monitor connected via VGA is not recognized

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98140

            Bug ID: 98140
           Summary: External monitor connected via VGA is not recognized
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: philipp.reinkemeier at offis.de
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

When connecting a beamer via VGA, this external monitor is not recognized. This
seems to be a regression of the i915 kernel driver. I am using archlinux, if
that matters. Using kernel 4.6.5 everything works as expected, but since kernel
4.7 things are broken. Also kernel version 4.8 does not work. The hardware is a
lenovo laptop T450s model, which has a VGA connector and display port. Display
resolution of the laptop panel is 1920x1080.

- Kernel 4.6.5, connecting via VGA to a beamer: Works and gives 1024x768
resolution.
- Kernel 4.7 or 4.8, connecting via VGA to a beamer: Does not work.
- Kernel 4.7 or 4.8, connecting via a VGA-to-display-port adapter to the
beamer: Does not work.
- Kernel 4.7 or 4.8, connecting via a HDMI-to-display-port adapter to the
beamer: Works and gives 1920x1080 resolution.

For the cases where the beamer is not recognized, the output of xrandr is as
follows:

Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
eDP1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis)
310mm x 170mm
   1920x1080     60.05*+
   1400x1050     59.98  
   1600x900      60.00  
   1280x1024     60.02  
   1280x960      60.00  
   1368x768      60.00  
   1280x720      60.00  
   1024x768      60.00  
   1024x576      60.00  
   960x540       60.00  
   800x600       60.32    56.25  
   864x486       60.00  
   640x480       59.94  
   720x405       60.00  
   640x360       60.00  
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

Interestingly, connecting to an ordinary monitor via the VGA port works and
gives a resolution of 1680x1050.

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