UART connected to DMA with char HAL API

It is also worth remembering that read/write require a data copy, it makes little difference to overall system performance if this is to/from the UART fifo, or from a memory buffer from which the UART will dma data. In both cases writes will eventually hit 'buffer full' and stall.

What you do need is a driver that does read/write directly to/from the fifo - rather than through another adaption layer! and a fifo that is big enough to buffer the required data.

I doubt that the Altera HAL driver meets either of these criteria. Also if you are trying to transfer data with low latency of cpu use then you'll need something more slim-line than the generic 'unix style' io functions.