USB display?

[Alan Cox]

On Mon, 12 Dec 2011 15:45:40 -0800
Alan Evans <ame.fedora at gmail.com> wrote:

> Hello All!
> 
> The boss dropped one of those DisplayLink USB display adaptors on my
> desk today, and I'm drooling at the prospect of having a third monitor
> on my devel machine.

Oh don't get too excited

> screen. But Xorg doesn't seem to care; and my desktop is still limited
> to my current two heads, with nary a hint of another display device
> available.

You need either
- A DisplayLink X server module

or

- Load the USB framebuffer driver (udlfb) with the option "fb_defio=1"
and add an xorg.conf for it. You may also need to fiddle with the
permissions on /dev/fb1 or wherever it ends up (udev can do this for you)

Now the bigger problem is that it's unaccelerated which means if you are
using Gnome 3 it'll drop the entire desktop back to the old style of
operation.

> In the old days, I might have tried to jack with the xorg.conf file,
> but that seems to have vanished somewhere along the way while I wasn't

xorg.conf still applies but the server defaults are for automatic probing
and behaviour.

> looking. Has anybody got one of these things to work? How can I tell
> Xorg that there's another display out there, longing to be used?

Write an xorg.conf just like the old days - put your USB interface in as
a fbdev device. Don't expect however to be able to drag windows between
the USB interface and the other monitors using a basic setup.

Gnome appears to be unable to cope with a single setup of unaccelerated
and accelerated displays in Gnome 3, so you may have to fiddle around a
bit or use a different desktop. Some people set the main desktop up
bigger than their displays and then run a separate server on the USB
display and use vnc full screen on it to display that extra chunk full
screen on a USB display. Hackish but works fine, and with minimal
performance impact.

Alan