Ben Widawsky had wrote some hardware context support patches more than a year ago, but now he's revised them and is calling for comments. Hardware context support is needed now in order to support OpenGL transform feedback in the presence of geometry shaders. The Intel graphics processors have supported hardware-based context switching going back to "Gen4" hardware through the latest Sandy Bridge and Ivy Bridge graphics processors.
As explained by Ben in this mailing list message, "HW contexts provide a way for the GPU to save an restore certain state in between batchbuffer boundaries. Typically, GPU clients must re-emit the entire state every time they run because the client does not know what has been destroyed since the last time. With these patches the driver will emit special instructions to do this on behalf of the client if it has registered a context, and included that with the batchbuffer."
This work could be a candidate for the Linux 3.4 kernel.