Chris released the xf86-video-intel 2.21.1 DDX driver on this Sunday morning. The original 2.21 driver enabled X RENDER support for Haswell GT1/GT2, brought multi-threaded rasterization for certain tasks, and supports a new kernel interface to be presented by the Linux 3.9 kernel.
The xf86-video-intel 2.21.1 release today cleans up some compilation warnings, minor build improvements, takes care of a potential i945GM (GMA 3100) GPU hang, prevents cache threashing and severe performance degradation on LLC machines, fixes alignment on sub-surface proxies for old chipsets, and repairs builds against X.Org Server 1.6 and contemporary packages. The fixes for old xorg-server releases and other older packages is for letting Intel SNA work on Debian 6.0 Squeeze.
In total there's 42 changes for the xf86-video-intel 2.21.1 point release, of which Chris Wilson committed 36 of the changes. The release announcement with details in full can be found on the xorg-announce list.