Airlie has been working on DisplayPort MST support for the open-source drivers. This DisplayPort 1.2+ feature allows daisy-chaining multiple DisplayPort displays off a single DP connector. DisplayPort MST is used by some 4K DisplayPort displays and it's also in use by some newer Lenovo ThinkPad Docks, which is why David Airlie has been exploring the support. David is primarily focused upon adding DisplayPort Multi-Stream Transport handling to the DRM/KMS Linux drivers.
The Linux DisplayPort MST code has been working for nearly one month and it's now undergoing further review by other upstream Linux DRM developers. Airlie wrote in a new mailing list post tonight, "So this set is pretty close to what I think we should be merging initially, Since the last set, it makes fbcon and suspend/resume work a lot better, I've also fixed a couple of bugs in -intel that make things work a lot better. I've bashed on this a bit using kms-flip from intel-gpu-tools, hacked to add 3 monitor support. It still generates a fair few i915 state checker backtraces, and some of them are fairly hard to work out, it might be we should just tone down the state checker for encoders/connectors with no actual hw backing them."
The DisplayPort MST patch-set primarily geared for Intel Linux graphics currently consists of 11 patches. Assuming all goes well, the DP 1.2 MST support for the open-source driver could happen for the Linux 3.16 kernel.