Back at the Linux Plumbers Conference in August, the Linux developers meeting in San Diego decided to create a CEC bus with CEC clients that is independent of the Video 4 Linux 2 and DRM APIs, so that both those sub-systems along with other "clients" could use this HDMI feature.
Consumer Electronics Control allows for controlling up to ten CEC-enabled devices connected via HDMI by using only one of the remote controls. CEC comes down to being a one-wire bi-directional serial bus built atop the AV.link protocol for remote control functionality.
HDMI CEC allows controls like controlling audio/video playback, system standby, one-touch recordings, timer programming, tuner control, system information, on-screen displays, routing control, and much more. Up to this point there hasn't been any unified support for HDMI CEC in the mainline Linux kernel.
The update on the Linux kernel CEC API support can be found here on the mailing list. Unfortunately the new CEC kernel bus isn't ready for Linux 3.7.