How on earth did Jellyfin get the RGA working on the 8 GB Zero3?
At last, I got it working, but it was a huge ordeal!
First, I had to recompile the Linux kernel to get an /dev/dma_heap/system-uncached-dma32.
Next, I had to manually allocate DMA memory for the RGA, using the example given by Rockchip. (https://github.com/airockchip/librga/blob/main/samples/allocator_demo/src/rga_allocator_dma32_demo.cpp)
Still, I face problems with allocating continuous memory for all my threads running the RGA.
In the end, the most simple and secure way was limiting the memory to 4 GB, in the /boot/extlinux/extlinux.conf (adding mem=4096M cma=256M).