[Libdlo] Tips for setting up displaylink with Xinerama

[B. Douglas Hilton]

I have a displaylink mini-monitor working quite well in conjunction
with a radeon graphics card. Here is a compact synopsis of what I did
to get it working.

Firstly, you need the newer udlfb sources which enable you to use the
xf86-driver-fbdev with Xorg. These can be fetched here:

"git clone http://git.plugable.com/webdav/udlfb"

To compile this, you will need to enable "Virtual Framebuffer" in your
kernel, and you will also want "VESA Framebuffer". Configuring vesafb
is beyond the scope here, but you want it to load up at boot time by
passing it a vga=0xNNN command appropriate for your primary display,
and be sure to select a 16-bit color depth.

Once booted, compile and install your new udlfb module, it must be
built against your running kernel so leave the source tree dirty.

When you modprobe the udlfb module you'll get a green screen. In the
future it should automatically load up to the green screen at boot
time. Having the VESA Framebuffer loaded by the kernel will prevent the
kernel from putting the console on the displaylink device.

Configure both devices in xorg.conf to use the "fbdev" driver. The
serverlayout section should look something like this:

Section "ServerLayout"
        Identifier     "X.org Configured"
        Screen      0  "RadeonScreen" 0 0
        Screen      1  "DisplayLinkScreen" LeftOf "RadeonScreen"
        Option         "Xinerama" "true"
        InputDevice    "Mouse0" "CorePointer"
        InputDevice    "Keyboard0" "CoreKeyboard"
EndSection

For my system, I have the following devices:

Section "Device"
        Identifier  "RadeonCard"
        Driver      "fbdev"
	Option      "fbdev" "/dev/fb0"
        VendorName  "ATI"
        BoardName   "Radeon HD-4830"
        BusID       "PCI:1:0:0"
EndSection

Section "Device"
        Identifier  "DisplayLinkDevice"
        Driver      "displaylink"
        Option      "fbdev" "/dev/fb1"
EndSection

Otherwise, follow standard procedure in setting up xorg.conf.

Look here for reference -> http://mulchman.org/blog/?p=21

You should also set both screen sections to Depth 16 so that they
match. If you have done everything right, and you're lucky, you should
be able to start up X and have a nice Xinerama session spanning both
screens.

I found that Xfce4 did a nice job of detecting both screens, and
properly configuring them such that icons were located properly, etc.
Gnome did much more poorly, and I didn't test kde4 very thoroughly.

The downside of this all is that you are stuck with the slow fbdev
drivers for Xorg, but at least it all works. I tried various
combinations of using the other xservers, including the accelerated
displaylink server, but they didn't play nice together and typically
caused segmentation fault crashes at best, and locked up the system at
worst.