The user ptr support was initially spearheaded by Intel OTC developers and has landed in their open-source driver. The focus of this work is to allow turning a memory pointer supplied by user-space into a buffer object for the graphics driver. This user ptr support is useful for GPGPU/compute scenarios and other situations for feeding memory objects to the GPU.
Christian's proposed patch for adding user ptr support to the Radeon DRM driver can be found on the DRI development list. This feature for the open-source AMD Linux driver next has a chance of premiering with the Linux 3.17 kernel.