DMA vs MSGDMA

This example is probably worth looking at, it's a bare metal program but it give you an idea what has to happen at a low level to communicate with the DMA core: https://www.altera.com/support/support-resources/design-examples/soc/fpga-to-hps-bridges-design-example.html

Those DMAs are performing ST-to-MM and MM-to-ST transfers so that's why the descriptor doesn't have a source and destination location.