David Airlie at Red Hat has been working on the DisplayPort Multi-Stream Transport support for some months by the open-source Linux graphics stack. Multi-Stream Transport was added to DisplayPort 1.2 to allow daisy-chaining multiple monitors to a single DisplayPort connector. In the context of this early open-source work, the DisplayPort MST work is mostly aimed around ThinkPads and other laptops that have a dock for exposing an external monitor via DP MST.
The most recent patches under review were publicized last month while David has now published a new patch-set targeting the Intel DRM driver. Airlie wrote on Wednesday, "Another round of the MST support for i915 haswell...The main fix is not talking to devices if HPD isn't asserted, at least on the dock I have it will reply to DPCD without HPD being asserted but it just confuses everyone. Otherwise it contains a bunch of stability fixes, and avoids the worst backtraces of i915 state tracker, which is fine when hw is involved but MST doesn't really fit so well with it, esp when you hot unplug some hardware, and the state tracker expects it to remain in the same state until userspace catches up, (note the hw is gone!)."
This Intel DisplayPort MST support is most likely too late to make it for Linux 3.16 but we can hope this DisplayPort improvement will make it for the Linux 3.17 kernel.