The Armada DRM driver isn't officially sanctioned by Marvell but written by Russel King of the ARM Linux community. The Armada DRM driver has TDA998x HDMI output support and designed for the Armada 510 and other hardware. In the latest patch-set, Russel King noted, "I believe all the major issues have been addressed now." This may mean it could be ready for inclusion into the Linux 3.13 kernel.
The Armada DRM driver supports multiple contiguous scanout buffers, SHM-backed cacheable buffer objects for X pixmaps and Vivante GPU acceleration, dual LCD operation, video overlays via DRM planes, page-flipping for main scanout buffers, ARGB hardware cursors, and DRM PRIME for buffer export/importing. While the Armada 510 is the support target, it should be trivial to support Marvell's other model SoCs. The TDA1998X HDMI output is for Solid-Run CuBox devices.