On 31-07-20, 23:08, Serge Semin wrote: > After a lot of tests and thorough DW DMAC databook studying we've > discovered that the driver can be optimized especially when it comes to > working with non-memory peripherals. > > First of all we've found out that since each DW DMAC channel can > be synthesized with different parameters, then even when two of them > are configured to perform the same DMA transactions they may execute them > with different performance. Since some DMA client devices might be > sensitive to such important parameter as performance, then it is a good > idea to let them request only suitable DMA channels. In this patchset we > introduce a functionality, which makes it possible by passing the DMA > channels mask either over the "dmas" DT property or in the dw_dma_slave > platform data descriptor. > > Secondly FIFO-mode of the "FIFO readiness" criterion is more suitable for > the pure memory DMA transfers, since it minimizes the system bus > utilization, but causes some performance drop. When it comes to working with > non-memory peripherals the DMA engine performance comes to the first > place. Since normally DMA client devices keep data in internal FIFOs, any > latency at some critical moment may cause a FIFO being overflown and > consequently losing data. So in order to minimize a chance of the DW DMAC > internal FIFO being a bottle neck during the DMA transfers to and from > non-memory peripherals we propose not to use FIFO-mode for them. > > Thirdly it has been discovered that using a DMA transaction length is > redundant when calculating the destination transfer width for the > dev-to-mem DMA communications. That shall increase performance of the DMA > transfers with unaligned data length. > > Finally there is a small optimization in the burst length setting. In > particular we've found out, that according to the DW DMAC databoot it's > pointless to set one for the memory peripherals since they don't have > handshaking interface connected to the DMA controller. So we suggest to > just ignore the burst length config when it comes to setting the memory > peripherals up. Applied all, thanks -- ~Vinod
