There's still quite a bit of work left before kernel mode-setting will be stable, but the patches can be found on the DRI development mailing list. These patches need to sit atop the recent GTT (Graphics Translation Table) mapping and EXA pixmap management patches.
Jesse has also sent along the Radeon driver that adds DRM/KMS mode-setting support (mailing list message), but it's currently out of date.
For more information on kernel mode-setting support for Linux, checkout A Preview of Kernel-based Mode-Setting and The State of Kernel Mode-Setting. Additionally, you may be interested in Red Hat's Plymouth and Fedora 10, which are KMS friendly.
Introduced in the Linux 2.6.28 kernel is GEM support for providing a kernel memory manager to the X.Org graphics drivers, which is a pre-requisite for kernel mode-setting. Intel had developed the Graphics Execution Manager after having a falling out over Tungsten's TTM.
Also available is the patches for core KMS support and the Intel i915 KMS driver.