Messages in this thread | | | Date | Mon, 3 Oct 2011 11:54:23 +0530 | Subject | Re: [PATCHv4] DMAEngine: Define interleaved transfer request api | From | Jassi Brar <> |
| |
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. [BTW, the scheme is broken because the dmac driver can't know if the client mapped the buffers with DMA_TO/FROM_DEVICE or with DMA_BIDIRECTION (dmatest.c does so)]
The only use of 'enum dma_data_direction' in DMAEngine _api_ is in 'struct dma_slave_config', device_prep_slave_sg and device_prep_dma_cyclic. Where too the dmac drivers disregard any value other than DMA_TO_DEVICE and DMA_FROM_DEVICE and very rightly so IMO.
So replacing dma_data_direction usage with xfer_direction in dmaengine is the best thing to do.
I don't know how better could I explain. If you still think otherwise, please do tell exactly when would a client need to use both the flags - dma_data_direction and xfer_direction?
>> > How could we have two macro names: SRC_MEM, DEST_MEM for mapping. or just add: >> > dma_map_single_src >> > dma_map_single_dst >> Not sure what you mean by this. > > my point is dma_data_direction is named wrong after we have your > xfer_direction. people will think dma_data_direction just means dma is > transferred from where to where. doesn't dma_data_direction mean m2d, > m2m, d2d, d2m just from the name? but actually it is just the mapping > direction now. > So basically you mean people might get confused because of 'dma_data_direction' and 'xfer_direction' names. The concern might or might not be serious, but it certainly doesn't warrant any change to dma_data_direction.
-j -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |