David Airlie at Red Hat has started merging some of his DisplayPort Multi-Stream (DP MST) support code into his drm-next branch for eventual merging into Linux 3.17. David has been hacking on the code for several months and has basic DP MST working on Linux -- the Multi-Stream Transport support is for daisy-chaining multiple DisplayPort connections, as needed by some 4K displays and other setups, and for David's main Linux use-case is the technology is used by some recent Lenovo ThinkPad dock setups. David's testing has been mostly centered around a Haswell-class Lenovo ultrabook with MST-based dock for its external graphics.
The DP MST code has been under review by open-source developers and is starting towards the next stage of mainline integration. So far though for drm-next is the multi-stream helper code that was merged a few hours ago.
On a separate note, worth pointing out for another merge into drm-next is UDL vBlank support and UDL page-flip ioctl support. UDL is the DisplayLink open-source DRM driver for the USB VGA devices. Also worth noting is that universal planes are no longer experimental with this next kernel release cycle.
Stay tuned for more coverage of Linux DRM graphics driver improvements for Linux 3.17 in the weeks ahead.