DisplayLink

DisplayLink is a technology that enables monitors to work via USB. In general the local GPU renders the picture, the frambuffer device compresses the data and sends it to the external device via USB.

Note: There is a new DRM_UDL driver for this hardware, merged into the 3.4 release cycle. I have not gotten it to work yet, even with the xf86-video-modesetting X11 driver.

Also, you can use the xf86-video-fbdev driver as well.

Installation
Enable the DisplayLink framebuffer device in your kernel:

After booting into the new kernel the external monitor should show a green background image. That means the kernel module is loaded and the device works, it also creates the device in /dev/fb0.

The X driver x11-drivers/xf86-video-displaylink is only available in the X11 overlay. Assuming layman is already configured, you add it with the following command:

Then update your /etc/make.conf with the new graphics card:

One X-Server
TODO

Two X-Server
This method is failsafe and should work with any graphics card installed. We start two instances of X-Server for each device and then use a software called x2x to move the input devices between them.
 * two independent instances and desktops
 * Input devices follow the mouse pointer

Software
For this method, we need another input device driver called :

The program is available in portage and can be installed via:

xorg.conf.DL
We configure two independent /etc/X11/xorg.conf for each device and initialize the desktop using ~/.xinitrc scripts. Create this file in /etc/X11/ and name it xorg.conf.DL:

.xinitrc2
Next we create the ~/.initrc2 for our external display. Create and customize the file to your needs, here is an example:

displaylink.sh
This is the actual script that starts the second instance of xorg-server. Make it executeable and save it somewhere in your home folder, in this example we save it to ~/.displaylink.sh

Links

 * libdlo freedesktop.org
 * Linux Forum displaylink.org
 * Linux plugable.com
 * Setting up Multiseat plugable.com