DisplayLink

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DisplayLink devices on Linux still only have experimental support. While some people have had success in using them, it is generally not an easy process and not guaranteed to work. The steps on this page describe the generally most successful methods of using external monitors with DisplayLink.

Also be warned that even over USB 3.0, a DisplayLink monitor may exhibit noticeably more lag than e.g. a DisplayPort monitor, especially when large portions of the screen are being redrawn.

Installation

USB 2.0 DL-1xx Devices

The kernel DRM driver for DisplayLink is udl, a rewrite of the original udlfb driver. It allows configuring DisplayLink monitors using Xrandr.

First, the setup and installation:

  • Blacklist the old kernel module, udlfb, which may attempt to load itself first.

USB 3.0 DL-5xxx, DL-41xx, DL-3x00 Devices

  1. Install the displaylinkAUR driver. It allows configuring DisplayLink monitors using Xrandr in the same manner as the udl driver.
  2. Enable displaylink.service.

Setting up X Displays

After that, run:

$ xrandr --listproviders
Providers: number : 2
Provider 0: id: 0x49 cap: 0xb, Source Output, Sink Output, Sink Offload crtcs: 2 outputs: 8 associated providers: 0 name:Intel
Provider 1: id: 0x13c cap: 0x2, Sink Output crtcs: 1 outputs: 1 associated providers: 0 name:modesetting

In the above output, we can see that provider 0 is the system's regular graphics provider (Intel), and provider 1 (modesetting) is the DisplayLink provider. To use the DisplayLink device, connect provider 1 to provider 0:

$ xrandr --setprovideroutputsource 1 0

and xrandr will add a DVI output you can use as normal with xrandr. This is still experimental but supports hotplugging and when works, it is by far the simplest setup. If it works then everything below is unnecessary.

Configuration

These instructions assume that you already have an up and running X server and are simply adding a monitor to your existing setup.

Load the framebuffer device

Before your system will recognize your DisplayLink device, the udl kernel module must be loaded. To do this, run

# modprobe udl

If your DisplayLink device is connected, it should show some visual indication of this. Although a green screen is the standard indicator of this, other variations have been spotted and are perfectly normal. Most importantly, the output of dmesg should show something like the following, indicating a new DisplayLink device was found:

usb 2-1.1: new high-speed USB device number 7 using ehci-pci
usb 2-1.1: New USB device found, idVendor=17e9, idProduct=03e0
usb 2-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 2-1.1: Product: Lenovo LT1421 wide
usb 2-1.1: Manufacturer: DisplayLink
usb 2-1.1: SerialNumber: 6V9BBRM1
[drm] vendor descriptor length:17 data:17 5f 01 00 15 05 00 01 03 00 04
udl 2-1.1:1.0: fb1: udldrmfb frame buffer device
[drm] Initialized udl 0.0.1 20120220 on minor 1

Furthermore, /dev should contain a new fb device, likely /dev/fb1 if you already had a framebuffer for your primary display.

To automatically load udl at boot, create the file udl.conf in /etc/modules-load.d/ with the following contents:

/etc/modules-load.d/udl.conf
udl

For more information on loading kernel modules, see Kernel modules#Automatic module handling.

Configuring X Server

Use xrandr or your Desktop Environment's display setup UI to configure your USB monitors running either the udl or displaylink driver.

xrandr

Once the driver is loaded, the DisplayLink monitor is listed as an output provider:

$ xrandr --listproviders
Providers: number : 2
Provider 0: id: 0x43 cap: 0xb, Source Output, Sink Output, Sink Offload crtcs: 2 outputs: 2 associated providers: 1 name:Intel
Provider 1: id: 0xcb cap: 0x2, Sink Output crtcs: 1 outputs: 1 associated providers: 1 name:modesetting

In the above example, provider 1 is the DisplayLink device, and provider 0 is the default display. Running xrandr --current gives a list of available screens:

$ xrandr --current
Screen 0: minimum 320 x 200, current 1600 x 900, maximum 8192 x 8192
LVDS1 connected 1600x900+0+0 (normal left inverted right x axis y axis) 309mm x 174mm
   1600x900       60.0*+   40.0  
   1440x900       59.9  
   1360x768       59.8     60.0  
   1152x864       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected (normal left inverted right x axis y axis)
DVI-1-0 connected (normal left inverted right x axis y axis)
   1366x768       60.0 +
   1368x768_59.90   59.9  
  1368x768_59.90 (0xd0)   85.7MHz
        h: width  1368 start 1440 end 1584 total 1800 skew    0 clock   47.6KHz
        v: height  768 start  769 end  772 total  795           clock   59.9Hz

If the above does not list the DisplayLink screen, then you will need to offload DisplayLink to the main GPU:

xrandr --setprovideroutputsource 1 0

Once the screen is available, refer to Xrandr for info on setting it up. For automating the configuration process, see displaylink.sh.

Enabling DVI output on startup

The DisplayLink provider will not be automatically connected to the main provider in most cases, therefore the DVI output device will not be available. It can be helpful to automatically do this when X starts to facilitate automatic display configuration by the window manager.

Edit your desktop manager's startup configuration and add commands similar to:

$(xrandr --listproviders | grep -q "modesetting") && xrandr --setprovideroutputsource 1 0

For example, the appropriate startup configuration file for SDDM is /usr/share/sddm/scripts/Xsetup.

Avoid placing these commands in ~/.xprofile as this breaks the display configuration of some window managers. Instead these commands should be run prior to any display output or setup.

Note: If you have additional providers, specify the name of the provider instead of using indexes. The name of the DisplayLink device will be modesetting

Troubleshooting

Not working configuration

These are tested on Xfce using Display settings (included in XFCE4 package) and external tool - arandr. XFCE4 Display settings are likelly to crash, so ARandR might help.

When you connect display link device via USB to your computer, the computer should show monitors in Display settings. There are few troubleshooting steps that you should try:

  • Check #Setting up X Displays. If you can find any external monitors recognized, you should try to make them visible by the following commands:
xrandr --setprovideroutputsource 1 0
xrandr --setprovideroutputsource 2 0
xrandr --setprovideroutputsource 3 0
...

This will make them visible and recognized in Display settings.

  • Restart displaylink.service.
  • Re-connecte USB cable.
  • Check if udl driver is loaded and monitors are connected.

Screen redraw is broken

If you are using udl as your kernel driver and the monitor appears to work, but is only updating where you move the mouse or when windows change in certain places, then you probably have the wrong modeline for your screen. Getting a proper modeline for your screen with a command like

gtf 1366 768 59.9

where 1366 and 768 are the horizontal and vertical resolutions for your monitor, and 59.9 is the refresh rate from its specs. To use this, create a new mode with xrandr like follows:

xrandr --newmode "1368x768_59.90"  85.72  1368 1440 1584 1800  768 769 772 795  -HSync +Vsync

and add it to Xrandr:

xrandr --addmode DVI-0 1368x768_59.90

Then tell the monitor to use that mode for the DisplayLink monitor, and this should fix the redraw issues. Check the Xrandr page for information on using a different mode.

If this does not solve the problem (or if the correct modeline was already in place because of correct DDC data), it can help to run a compositor. E.g. when using plain i3, running xcompmgr or compton can mitigate the problem.

DisplayLink refresh rate is extremely slow with gnome 3

If once you set up your DisplayLink your entire desktop becomes slow, try setting a "simpler" background image, such as complete black.

See Also