The XA state tracker has been primarily developed by VMware for their VMwgfx Linux graphics driver with Gallium3D. However, recently the Freedreno driver has begun using XA for accelerating 2D with this open-source, reverse-engineered Qualcomm graphics driver.
Rob Clark, the lead Freedreno developer, published a set of patches that optimize XA's performance. Rob is working towards Freedreno GLAMOR support, but until that's in place, he's looking to optimize the XA code. These patches can be found on the Mesa-dev mailing list and are providing some significant performance improvements.
Rob wrote on the mailing list, "While still more of a stop-gap solution (until glamor) for freedreno, with these few relatively simple changes I get a pretty big performance boost (~40%) for xf86-video-freedreno."