3D support for Displaylink devices

[Alan Cox]

> The window system needs support for splitting rendering and display.
> In X these are currently tied together.  The only real obstacle is
> fixing this in X.  However, this is a lot of work.  Dave Airlie has
> started working on this, but it's not really usable yet.   See:
> http://airlied.livejournal.com/71734.html
> http://cgit.freedesktop.org/~airlied/xserver/log/?h=drvlayer

In the windows world it basically works by 'borrowing' the real graphics
card for rendering and then doing the damage list/compression/uplink.

So its basically a *very* strange CRTC/scanout. To most intents and
purposes plugging one into an i915 say is an extra i915 head, and indeed
you can sensibly display the same scanout buffer on both real and link
heads.

Alan