HDA Intel is widely-used for integrated sound adapters and providing HDMI/DisplayPort audio support. The Linux driver for HDA Intel supports around 50 different controllers and 300+ different codecs. Up to this point it's been a maintenance burden handling all of the differences in this audio kernel driver as part of ALSA, but it's to be largely improved with Linux 3.9.
With work done by SUSE's Takashi Iwai, the HDA kernel codec drivers will become largely unified. This unification will dramatically lower the maintenance burden of the Intel HDA support under Linux and will make it much easier for supporting new HDA-supported hardware. It's basically a new, generic driver.
The Realtek, C-Media, CA0110, and AD codecs will be initially merged and should be primed for the Linux 3.9 kernel. The Cirrus, Conexant, VIA, and IDT codec merging for this new generic support will follow but might not come until the Linux 3.10 kernel.
Canonical's David Henningsson has written some more in a blog post about these forthcoming HDA driver changes.