On Fri, 11 Mar 2016 11:54:52 +0530 Vinod Koul <vinod.k...@intel.com> wrote:
> On Wed, Mar 09, 2016 at 11:14:34AM +0100, Boris Brezillon wrote: > > > > > > > + * struct sun4i_dma_chan_config - DMA channel config > > > > > > > + * > > > > > > > + * @para: contains information about block size and time before > > > > > > > checking > > > > > > > + * DRQ line. This is device specific and only applicable > > > > > > > to dedicated > > > > > > > + * DMA channels > > > > > > > > > > > > What information, can you elobrate.. And why can't you use existing > > > > > > dma_slave_config for this? > > > > > > > > > > Block size is related to the device FIFO size. I guess it allows the > > > > > DMA channel to launch a transfer of X bytes without having to check > > > > > the > > > > > DRQ line (the line telling the DMA engine it can transfer more data > > > > > to/from the device). The wait cycles information is apparently related > > > > > to the number of clks the engine should wait before polling/checking > > > > > the DRQ line status between each block transfer. I'm not sure what it > > > > > saves to put WAIT_CYCLES() to something != 1, but in their BSP, > > > > > Allwinner tweak that depending on the device. > > > > > > we already have block size aka src/dst_maxburst, why not use that one. > > > > Okay, but then remains the question "how should we choose the real burst > > size?". The block size described in Allwinner datasheet is not the > > number of words you will transmit without being preempted by other > > master -> slave requests, it's the number of bytes that can be > > transmitted without checking the DRQ line. > > IOW, block_size = burst_size * X > > Thats fine, API expects words for this and also a width value. Client shoudl > pass both and for programming you should use bytes converted from words and > width. > Not sure I get what you mean. Are you suggesting to add new fields to the dma_slave_config struct to describe this block concept, or should we pass it through ->xxx_burstsize, and try to guess the real burstsize? In the latter case, you still haven't answered my question: how should we choose the burstsize? -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
