The Zynq UltraScale+ MPSoC integrates several ARM cores and an FPGA into a single chip. One variant of this SoC includes an H.264/H.265 Allegro DVT Video Codec Unit (VCU).
Although Xilinx did a good job supporting the ZynqMP in mainline Linux, the VCU was originally only supported via an out-of-tree driver. It consists of a user space library and a firmware blob, which interact via a custom IOCTL interface. Unfortunately, this has security implications as the user space handles physical buffer addresses.
Fortunately, the V4L2 mem2mem device API for video codecs avoids this problem by using abstract DMA buffers. Many applications already use these APIs, and various drivers for hardware codecs already implement these APIs. Thus, a V4L2 driver for the VCU allows reusing existing applications such as FFmpeg and GStreamer on the ZynqMP.