Here's the first shot at using a USB-based DisplayLink graphics adapter with Ubuntu 12.04 LTS.
As mentioned a few days ago,
Plugable gave me four of their multi-seat terminal clients to try out that they are currently offering on
Kickstarter to
have a $50 easy-to-use multi-seat experience. Two of the devices are the DC-125 with the DisplayLink DL-125 chipset while the other two are the UD-160-A with the DisplayLink DL-165 chipset that can output up to 1920 x 1080 over DVI or VGA.
In quickly wanting to try out one of the DC-125 USB graphics devices before
leaving, I wanted to see what would happen if using the multi-seat USB device on Ubuntu 12.04. All of the work Plugable has been doing and many of the other upstream developers have benefited Fedora 17 -- that's where the multi-seat experience is seamless.
Bernie Thompson, the founder of Plugable, is the upstream maintainer of the
DisplayLink FB driver in the mainline Linux kernel. This FB driver is soon going to be succeeded by the
DisplayLink KMS driver. However, aside from the DisplayLink FB/KMS graphics driver and the DisplayLink DDX driver, there's also other work that goes into making this multi-seat experience a reality.
Lennart Poettering of Red Hat made systemd changes to make this multi-seat experience more streamlined, and he even considers this work to be
the most awesome but least advertised feature of the Beefy Miracle. So it's known that Ubuntu 12.04 won't be a seamless Plugable multi-seat experience since they're not even touching systemd, but nevertheless I was curious about DisplayLink graphics on Ubuntu 12.04, since it does at least have the frame-buffer driver (
udlfb) as part of its kernel build.
The DisplayLink DL-125 ASIC only supports VGA and a maximum resolution of 1440x900 or 1280x1024, which limited the range of monitors that could be tested here at my home office... (At least the DL-165 supports DVI and resolutions up to 1920 x 1080.) But I still have two
Acer AL1715 displays, which are 1280 x 1024 VGA LCD panels that I've had for the past six years. (For those that always ask when seeing photos, the dual and quad LCD stands I use are
the Tyke Supply monitor stands and I highly recommend those over the more popular - and more expensive - Ergotron stands. The 17-inch Acer LCD is then clamped to the Tyke Supply dual LCD stand with a
Arctic Z1 stand.)
When booting Ubuntu 12.04 with its stock Linux 3.2 kernel and the DL-125 USB adapter connected to the 1280 x 1024 VGA display, the
udlfb driver was loaded automatically and the external display lit up, but the screen was just green...
As I had the Linux 3.3 and Linux 3.4 (development) kernels also installed due to other tests being run from this Intel Linux system, I also tried out the DisplayLink USB graphics hardware with the newer kernel and the frame-buffer driver there. The Acer LCD was no longer green and there was now text, but the frame-buffer driver reported that it was unable to get valid EDID from the display. This is rather interesting since in the six years of using this name-brand LCD for tests, it's never had EDID-related issues. This is a standard 1280 x 1024 panel and even with the old UMS-only X.Org drivers from six years ago, that never even hit any Extended Display Identification Data problems.
But even after claiming there was no valid EDID, the
udlfb driver was at least able to determine there was the 1280 x 1024 valid mode, but in the end it chose 800 x 600.
For now it looks like the best DisplayLink USB graphics experience on Linux is with Fedora 17. However, this will be continued after having more time to try out the hardware in different configurations.
