Messages in this thread | | | Date | Mon, 3 Oct 2011 10:15:16 -0700 | Subject | Re: [PATCHv4] DMAEngine: Define interleaved transfer request api | From | "Williams, Dan J" <> |
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On Mon, Oct 3, 2011 at 9:19 AM, Jassi Brar <jaswinder.singh@linaro.org> wrote: > On 3 October 2011 21:43, Russell King <rmk@arm.linux.org.uk> wrote: >> On Mon, Oct 03, 2011 at 11:54:23AM +0530, Jassi Brar wrote: >>> On 2 October 2011 06:03, Barry Song <21cnbao@gmail.com> wrote: >>> > 2011/10/2 Jassi Brar <jaswinder.singh@linaro.org> >>> >>> >> > For example, it can't use >>> >> > MEM_TO_MEM to map, it still need to know whether the memory is source >>> >> > or dest. >>> >> MEM_TO_MEM means "From Memory Source To Memory Destination" >>> >> Map Src buffer with DMA_TO_DEVICE and Dst buffer with DMA_FROM_DEVICE >>> >> >>> >> MEM_TO_DEV means "From Memory Source To FIFO Destination" >>> >> Map Src buffer with DMA_TO_DEVICE. >>> >> >>> >> DEV_TO_MEM means "From FIFO Source To Memory Destination" >>> >> Map Dst buffer with DMA_FROM_DEVICE >>> >> >>> >> DEV_TO_DEV means "From FIFO Source To FIFO Destination" >>> >> >>> >> What else would you want to know ? >>> > >>> > that is the problem. for example, drivers can't use MEM_TO_MEM as a >>> > flag to do dma mapping. so xfer_direction can't cover all that >>> > dma_data_direction can do. that's why you need both >>> > dma_data_direction and xfer_direction with some similar flags in them. >>> > >>> The client drivers map the src/dst buffers and the dmac driver unmaps >>> them by default(!). For which, the dmac driver doesn't look at anything >>> other than >>> DMA_COMPL_SKIP_SRC/DST_UNMAP >>> DMA_COMPL_SRC/DST_UNMAP_SINGLE >>> bits of 'enum dma_ctrl_flags'. >>> For this unmap'ing purpose, the usage of dma_data_direction is already >>> internal to the dmac driver. >> >> No. Slave DMA engine drivers do *not* (and if they do, they should *not*) >> honour the unmapping of submitted buffers. >> >> The unmapping of these buffers by the DMA engine driver is intended to be >> done for the async_tx API and not slave DMA. >> > The proposed api is usable by both Slave as well as Async(Memcpy etc). > So it *does* matter here.
I think the confusion is reduced if you don't try to use this api for mem-to-mem transfers. Then you can use DMA_NONE to indicate the dev-to-dev case. If a mem-to-mem user arrives we can revisit xfer_direction, but as it stands it seems this is primarily useful for slave-dma, i.e. I don't see async_tx_dma or net_dma switching to this scheme anytime soon, if ever. Are there other mem-to-mem use cases that would use this?
Also in dmaxfer_template I do not understand the need for src_inc and dst_inc. Aren't those properties that the client would know about the slave device?
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