I bought one of these of ebay -
DELTACO USB 2.0 till DVI/HDMI/VGA-adapter
Planning to use it on a custom x86 board I have, that doesn't have a graphics adapter. First trying it on Windows 7 - where it worked fine, after downloading and installing the drivers.
I then booted Linux, expecting to again download drivers, and likely need to compile them, with the usual dependency nightmares...
However, on boot, the display came up by itself :)
[ 16.823553] udl 5-2:1.0: fb1: udldrmfb frame buffer device
[ 16.823559] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[ 16.823561] [drm] No driver support for vblank timestamp query.
[ 16.823563] [drm] Initialized udl on minor 1
[ 16.823599] usbcore: registered new interface driver udl
Bus 005 Device 002: ID 17e9:0198 DisplayLink