Maarten Lankhorst has published some "request for comment" patches concerning DMA-BUF synchronization. "This patch implements my attempt at dmabuf synchronization. The core idea is that a lot of devices will have their own methods of synchronization, but more complicated devices allow some way of fencing, so why not export those as dma-buf? This patchset implements dmabufmgr, which is based on ttm's code. The ttm code deals with a lot more than just reservation however, I took out almost all the code not dealing with reservations."
Maarten's code introduces a dma-buf-mgr (manager) component, PRIME work-in-progress support for the i915 driver, extended Nouveau PRIME code, and Nouveau fence PRIME implementation. Maarten Lankhorst worked on this code as part of his official duties at Canonical, with their interest in supporting hybrid graphics / NVIDIA Optimus under Linux.
There's still much to do on the hybrid graphics front and it doesn't look like it will come together in any official capacity for Ubuntu 12.10, but at least the code is moving in the right direction.