* 3D accelerator, which is what some people call the GPU, but it only does 3D acceleration (OpenGL ES in most cases) and on newer models it can also run OpenCL - not the case on this SoC which has a Mali-400. This is working with closed source drivers on GNU/Linux.
* a video decoder and sometimes a video encoder, Hantro G1[0] and Hantro H1[1] on this hardware. These are unsupported on GNU/Linux, possibly because Android uses its libstagefright[2] infrastructure and there's limited demand for GNU/Linux support.
* sometimes a 2D accelerator, which would mostly be used for blits, resizing and rotation nowadays. RK3188 actually has two different units with overlapping functionality and which work on GNU/Linux with open source drivers.
Even though the video decoder is unsupported on GNU/Linux, the ARM cores are fast enough to decode 720p and (with some frame loss) 1080p h264 video. I wrote an XV driver[3] for RK3188 which uses hardware support for colorspace conversion and video resizing together with a few other tricks.
[0] http://www.verisilicon.com/IPPortfolio_14_58_2_HantroG1.html
[1] http://www.verisilicon.com/IPPortfolio_14_82_2_HantroH1.html