For months now there's been an Armada DRM/KMS graphics driver for Marvell Armada ARM SoCs. Having gone through several patch revisions, it appears that all major issues have now been addressed for this nearly 5,000 line open-source driver.
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.