[Libdlo] Fwd: xorg seqfault if main display is usb

[Bernie Thompson]

Hi Marcus,

On Tue, Apr 5, 2011 at 3:27 PM, Marcus Becker
<marcus.disi at googlemail.com> wrote:
> If I just use the displaylink device it works and I can use the screen on
> the usb monitor. Together with the nvidia it seqfaults again :(

The Linux plumbing in this area (multiple displays driven by multiple
adapters) is problematic.  It's a shame, because people coming from
Windows have expectations about multiple monitor behavior, and Linux
can't do that in the same way.

In theory, the old Xinerama X extension should be able to allow a
single desktop to span multiple X servers, but it appears to have many
problem areas in practice.

What does work is running multiple, independent X servers, as you're
thinking of doing.  It's very useful for multi-user (multiseat)
setups, like these:

* http://plugable.com/2009/11/16/setting-up-usb-multiseat-with-displaylink-on-linux-gdm-up-to-2-20/
* http://lucasnascferreira.wordpress.com/2010/07/13/tutorial-to-set-up-a-multiseat-with-plugable-dock-stations-gdm-2-27-consolekit-0-4-1-and-xorg-1-8-on-ubuntu-10-4/

And Alexander's recent work at

* http://otb.bg/blog/usb-multiseat-on-red-hat-enterprise-linux-6/252

So the low-level DisplayLink driver (the udlfb framebuffer driver)
works well enough, but at a higher level, trying to recreate the
Windows single-user multiple display setup with a mix of PCI and USB
graphics adapters is problematic.

Hope that helps in terms of realistic expectations on Linux.  Sorry
it's not an happier answer.

By the way, the udlfb doc in the kernel has some background:
http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=blob;f=Documentation/fb/udlfb.txt;h=7fdde2a02a27be74e7e45508e449b5376b28abca;hb=HEAD

Best regards,
Bernie