DP 1.2 / Daisychaining2 Monitors on Linux Mint / XPS13 2015

Question

I'am at the edge of giving up on my dual monitor (daisy chaining) setup with Linux Mint. I'm not quite sure if this problem is specific to Mint.

Setup:

• Dell XPS13 2015
• 2x Dell U2415

What I already did:

• Updated Kernal: 4.3.0-040300-generic
• Compiled Latest Intel Driver: xf86-video-intel
• Bios@A05

What's not happening:

• DP1 is not detected if the Display is set to DP 1.2

Story:

I wanted to test if a dual monitor setup with a laptop is becoming a possibility for work. When I first booted up with all displays connected ( XPS > Display 1 > Display 2 ) everything worked fine, but the displays were just mirrors of each other. After setting the Display 1 to "DP 1.2", I got an error on bootup. (Failed to start x-server .... jadajada). After googling and trying for hours, I had to install "xserver-xorg-dev" for the newest xorg-macros to compile the newest intel drivers with (xf86-video-intel). That removed the startup error, but the displays are still not visible in xrandr. After some more googling I upped from Kernel 4.0 to 4.3 - without luck. Disabling the DP 1.2 option shows the display in xrandr again, but still mirrored. I have confirmed with Dell support, that the XPS13 2015 should be able to do MST/DP1.2a, but I seem to fail.

Hope to get some love, G.

PS: I've found:

• https://askubuntu.com/questions/369946/displayport-1-2-mst-daisy-chain-dual-monitor-setup-intel-graphics
• https://askubuntu.com/questions/591731/dell-xps-13-2015-ubuntu-compatibility-displayport-mst

but the answers are either outdated or don't solve my problems!

Answer 1

I have a similar setup: DELL XPS12 (2014) & 2x DELL 2414h. Currently I am running Ubuntu 15.10, but had this setup since 15.04. With 15.04 I always had to modify ~/.config/monitors.xml as one of the monitors was not detected on the right address/bus. I think it always used DP1 and DP1-1, different that the output of the xrandr command. With 15.10 I don't have to manually modify that however the second display in the chain is not stable as it flickers from time to time.

The output of xrandr for me is now this:

Screen 0: minimum 8 x 8, current 3840 x 1080, maximum 32767 x 32767
eDP1 connected (normal left inverted right x axis y axis)
   1920x1080     59.93 +
   1680x1050     59.95    59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1600x900      60.00  
   1280x1024     60.02  
   1440x900      59.89  
   1280x960      60.00  
   1368x768      60.00  
   1360x768      59.80    59.96  
   1152x864      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)
DP1-1 connected primary 1920x1080+1920+0 (normal left inverted right x axis y axis) 527mm x 296mm
   1920x1080     60.00*+  50.00    59.94  
   1600x1200     60.00  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.08    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
DP1-2 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 527mm x 296mm
   1920x1080     60.00*+
   1600x1200     60.00  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1024x768      75.08    60.00  
   800x600       75.00    60.32    56.25  
   848x480       60.00  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
HDMI1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

And my monitors.xml is:

<monitors version="1">
  <configuration>
      <clone>no</clone>
      <output name="eDP1">
          <vendor>LGD</vendor>
          <product>0x03fd</product>
          <serial>0x00000000</serial>
      </output>
      <output name="DP1">
      </output>
      <output name="DP1-1">
          <vendor>DEL</vendor>
          <product>0xa0a3</product>
          <serial>0x3047484c</serial>
          <width>1920</width>
          <height>1080</height>
          <rate>60</rate>
          <x>1920</x>
          <y>0</y>
          <rotation>normal</rotation>
          <reflect_x>no</reflect_x>
          <reflect_y>no</reflect_y>
          <primary>yes</primary>
      </output>
      <output name="DP1-2">
          <vendor>DEL</vendor>
          <product>0xa0a2</product>
          <serial>0x3654344c</serial>
          <width>1920</width>
          <height>1080</height>
          <rate>60</rate>
          <x>0</x>
          <y>0</y>
          <rotation>normal</rotation>
          <reflect_x>no</reflect_x>
          <reflect_y>no</reflect_y>
          <primary>no</primary>
      </output>
      <output name="HDMI1">
      </output>
      <output name="VIRTUAL1">
      </output>
  </configuration>
</monitors>

Answer 2

I am successfully running a MST DisplayPort daisy-chain setup on my Haswell-based Dell Latitude E7240, with a new Dell 27" and an older HP 24" monitor daisy-chained through the Dell one.

Initially I had issues because the new Dell monitor was by default configured to terminate the DP connection(MST was off in the monitor settings), and I had to enable it there.

I still have an annoying bug, though: randomly each of the monitors turns black every now and then for a split-second, and I have no fix for this yet.

I am running Ubuntu 16.04 and I just happen to have a manually installed 4.7.0 kernel from the http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.7 but that may not be needed for the daisy-chain. I just installed it a few weeks before(I think it was 4.7.0-rc5 back then) for another reason, also related to the Intel driver: my laptop's screen also used to similarly turn off for a split-second, and that issue was fixed in 4.7.0.