This is an older graphics core used in early Galaxy devices. There is work on an open source driver (openfimg).
Work continues on a basic KMS driver (git) has been merged into the mainline linux kernel since 3.2 but this does not provide any 3D acceleration.
There is work on an open source driver (Lima git) for the Mali GPU that is used in all recent Exynos versions.
ARM is working on a unified KMS driver structure for most ARM SoC that will handle modesetting and 2D with an X component. Then load a binary blob to drive proprietary parts, such as their Mali GPU. An approch they borrowed from OMAP.
An open source frame buffer driver for Tegra2 chips shows up on the dri-devel mailing list. As of 3.6-rc1 the source is not yet in the mainline linux kernel though there appear to be plans for future inclusion.
There is also an Nvidia produced driver for X on Ubuntu.
There was a driver from Qualcomm, but it doesn't seem to have advanced anywhere.
Instead there is now an open source driver (freedreno git) for the Adreno GPUs that is currently being worked on and is making progress.
Texas Instruments (OMAP)
A KMS driver for simple modesetting is included in the staging area of the kernel since version 3.2. This driver does not provide 3D support though there may be plans to add support for loading a binary blob. There is also an X driver (git).
Atom SoC with PowerVR graphics.
The next generation Atom SoC, will likely use Ivy Bridge graphics which has open source drivers.
We will find out soon.
Android GPU Drivers
Example of an Android driver being used on the Touchpad with Mer.