Difference between revisions of "DisplayLink"

From ArchWiki
Jump to: navigation, search
(See Also: Corrects typo)
(Load the framebuffer device: FILES section no longer needed, formatting improvements in code block)
Line 42: Line 42:
To automatically load {{ic|udlfb}} at boot, add it to your {{ic|MODULES}} array in {{ic|mkinitcpio.conf}}.
To automatically load {{ic|udlfb}} at boot, add it to your {{ic|MODULES}} array in {{ic|mkinitcpio.conf}}.
{{hc|/etc/mkinitcpio.conf|2=MODULES="... '''udlfb''' ..."
{{hc|/etc/mkinitcpio.conf|2=MODULES="... udlfb ..."}}
Then, rebuild the kernel image:
Then, rebuild the kernel image:

Revision as of 19:38, 9 June 2013

The following steps are the most recent ones that the DisplayLink support guy was suggesting. I packaged the revisions in AUR, that compiled and worked great so far. According to the Plugable information they should work with almost every DisplayLink (DL-1**) device although they do not suggest using their devices with Linux for production use for now.


Install the xf86-video-fbdev package, which provides framebuffer video for X.org.

Hardware-level support is provided by the kernel module udlfb, which should be loadable by default in Arch.

Note: Support for the features in xf86-video-fbdev-for-displaylinkAUR and udlfbAUR from the AUR have been included upstream and are no longer needed. Use the official packages instead.


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 udlfb kernel module must be loaded. To do this, run

# modprobe udlfb

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 2-1.2: new high-speed USB device number 5 using ehci-pci
udlfb: DisplayLink Lenovo LT1421 wide - serial #6V9BBRM1
udlfb: vid_17e9&pid_03e0&rev_0108 driver's dlfb_data struct at ffff880231e54800
udlfb: console enable=1
udlfb: fb_defio enable=1
udlfb: shadow enable=1
udlfb: vendor descriptor length:17 data:17 5f 01 0015 05 00 01 03 00 04
udlfb: DL chip limited to 1500000 pixel modes
udlfb: allocated 4 65024 byte urbs
udlfb: 1366x768 @ 60 Hz valid mode
udlfb: Reallocating framebuffer. Addresses will change!
udlfb: 1366x768 @ 60 Hz valid mode
udlfb: set_par mode 1366x768
udlfb: DisplayLink USB device /dev/fb1 attached. 1366x768 resolution. Using 4104K framebuffer memory

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

To automatically load udlfb at boot, add it to your MODULES array in mkinitcpio.conf.

MODULES="... udlfb ..."

Then, rebuild the kernel image:

# mkinitcpio -p linux

For more information on this, see Mkinitcpio.

Update Xorg.conf

You must update or create an xorg.conf with a properly configured ServerLayout to use a DisplayLink monitor, as Xorg will prefer internal monitors by default. The DisplayLink device is normally only usable if it is set as screen0 and the internal display as screen1.

Add this to the bottom of xorg.conf:

################ DisplayLink Stuff ###################
Section "Device"
       Identifier      "DisplayLinkDevice"
       Driver          "fbdev"
       BusID           "USB"               # needed to use multiple DisplayLink devices 
       Option          "fbdev" "/dev/fb0"  # change to whatever device you want to use
#      Option          "rotate" "CCW"      # uncomment for rotation

Section "Monitor"
       Identifier      "DisplayLinkMonitor"

Section "Screen"
       Identifier      "DisplayLinkScreen"
       Device          "DisplayLinkDevice"
       Monitor         "DisplayLinkMonitor"
       DefaultDepth    16

Then edit your server layout to look something like this

Screen		0	"DisplayLinkScreen"
Screen		1	"Internal" RightOf "DisplayLinkScreen"
Option		"Xinerama" "on"

Change Internal to your main display, then restart X.


X crashes or keeps blank

If X crashes, or nothing is shown at load, try to start X only using the external display by updating xorg.conf as follows:

 Screen		0	"DisplayLinkScreen"
 #Screen		1	"Internal" RightOf "DisplayLinkScreen"
 #Option		"Xinerama" "on"

There are reported instances in which Xinerama requires all its Screen color depths to be the same. In both Screen sections, try changing the DefaultDepth to 16.

Section "Screen"
    DefaultDepth    16

Note: With fbdev this is not true anymore, because fbdev provides virtual 24 bit support. Everything may be used with DefaultDepth 24. However, USB 2.0 has less bandwidth than a standard monitor, so a performance update may be seen from setting it to 16 bit mode.

Cannot start in framebuffer mode. Please specify busIDs for all framebuffer devices

With two monitors configured in Xinerama mode, /var/log/Xorg.0.log will sometimes display the following error:

Fatal server error:
Cannot run in framebuffer mode. Please specify busIDs for all framebuffer devices

As indicated by this Gentoo Forums thread, KMS might be incompatible with fbdev. They also suggested the possible fix of running startx -- -retro which will allow X to run even when, to X itself, it doesn't appear to be working.

Note: A bug report has been filed for this issue.

See Also