I was embarrassed to discover that the ever-popular dlfb “green screen” is broken in subtle ways by the new defio support. So for now with this new driver, DL devices may up with what appears to be gibberish. I didn’t notice, because my test config launches X on the DisplayLink device immediately.
In the absence of a working X setup, and until the draw-during-probe issue is resolved, another great way to confirm your DL devices are working properly is with the fbi (“linux framebuffer imageviewer”) utility.
sudo apt-get install fbi
Run the above to install fbi (on Ubuntu/Debian).
fbi -d /dev/fb0 -a *.jpg
And this to show a full-screen slideshow with fbi — replacing “/dev/fb0” with one of your DisplayLink devices. You can “ls /sys/class/graphics/” to see all your framebuffer devices, and look within those directories for details on them. Of course, run the fbi utility from a directory with some jpgs (or other images) to display. pg-up/pg-down to move between photos.
You must run the fbi program from a console (fbi limitation). So hit Ctrl-Alt-F1 or something first, login from that text console, and run from there.
This wouldn’t work with older versions of udlfb or displaylink-mod (without defio support), and it makes a nice new test case. Now, short instructions for getting mplayer working for fbdev video would be welcome …