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.

The machine is running F14 at present and the kernel doesn't know what
to do with the adapter when I plug it in. The system log indicates
that something with a particular vendor ID is plugged in but nothing
else. These things are pretty new so I booted a F16 Live CD and the
situation is much better. The system log enumerates available
resolutions, allocates a framebuffer, and registers the udlfb driver
for it. The monitor, for its part, presents a lovely solid green
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.

This all seems so close I can taste it. But I don't know what to try.

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
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?

-Alan
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On Mon, 12 Dec 2011 15:45:40 -0800
Alan Evans <ame.fedora@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

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