On Thu, Aug 10, 2017 at 12:44 PM, Dave Jiang <dave.jiang@xxxxxxxxx> wrote: > > > On 08/10/2017 12:05 PM, Dan Williams wrote: >> On Thu, Aug 10, 2017 at 9:22 AM, Dave Jiang <dave.jiang@xxxxxxxxx> wrote: >>> >>> >>> On 08/09/2017 07:20 PM, Dan Williams wrote: >>>> On Wed, Aug 9, 2017 at 7:15 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >>>>> On Mon, Aug 7, 2017 at 9:39 AM, Dave Jiang <dave.jiang@xxxxxxxxx> wrote: >>>>>> In preparation of adding an API to perform SG to/from buffer for dmaengine, >>>>>> we will change DMA_SG to DMA_SG_SG in order to explicitly making clear what >>>>>> this op type is for. >>>>>> >>>>>> Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx> >>>>>> --- >>>>>> Documentation/dmaengine/provider.txt | 2 +- >>>>>> drivers/crypto/ccp/ccp-dmaengine.c | 2 +- >>>>>> drivers/dma/at_hdmac.c | 8 ++++---- >>>>>> drivers/dma/dmaengine.c | 2 +- >>>>>> drivers/dma/dmatest.c | 12 ++++++------ >>>>>> drivers/dma/fsldma.c | 2 +- >>>>>> drivers/dma/mv_xor.c | 6 +++--- >>>>>> drivers/dma/nbpfaxi.c | 2 +- >>>>>> drivers/dma/ste_dma40.c | 6 +++--- >>>>>> drivers/dma/xgene-dma.c | 4 ++-- >>>>>> drivers/dma/xilinx/zynqmp_dma.c | 2 +- >>>>>> include/linux/dmaengine.h | 2 +- >>>>>> 12 files changed, 25 insertions(+), 25 deletions(-) >>>>> >>>>> Given the prevalence and age of DMA_SG I think we should call the new >>>>> op DMA_SG_SINGLE, or something like that, so that we don't surprise >>>>> someone who was expecting the old command type. >>>> >>>> Oh wait, you already call the new op DMA_MEMCPY_SG, so why does the >>>> old one need to change? ...and thinking about it further why do we >>>> need a new op at all? Couldn't we just pass in a single entry >>>> scatterlist that was setup on the stack with memcpy target address? >>> >>> That would probably work if we can do dma_map_sg() before submit and >>> dma_unmap_page() on completion since we'll lose the sg entry. I also >>> have concerns with the DMA_SG function provided in the ioatdma driver >>> since it really doesn't do scatter gather and it's all software >>> abstracted. It's not a big deal to support a single entry SG, but it >>> wouldn't be supporting real SG to SG setup without more complex code. I >>> worry about the overhead and messiness of it. Of course if you are ok >>> with providing a DMA_SG function that really doesn't do exactly what >>> it's advertised to do and only cater to pmem usage. >> >> I'm fishing for a way to not to make the dmaengine operation-type >> proliferation problem worse. The sg-to-sg operation is odd in that >> typical usages of a scatterlist have a contiguous buffer as the source >> or destination. A change that gets us closer to that typical model is >> what I'm looking for and not adding baggage that we need to unwind >> later since everyone seems to agree that this "->prep_X() + >> ->submit()" model is broken. I'd like to revisit whether we actually >> need sg-to-sg vs that typical sg-to-buf model, and once we have the >> typical model can we refactor all commands to use a single entry point >> to the driver that takes a single scattler list parameter (similar to >> scsi, usb, etc). > > Looking through the kernel it does not look like there's an actual in > kernel consumer for DMA_SG. That makes it rather difficult to determine > what it's used for. I have a feeling its usage is out of tree and thus > explain the deviation from typical kernel usages. I'm wondering if we > should to introduce DMA_SG_MEMCPY to set that as the standard and then > deprecate DMA_SG eventually. If there are no in-tree consumers of DMA_SG we can deprecate it immediately. This is standard process (Documentation/process/stable-api-nonsense.rst). When / if someone notices this missing, they can work to get their use case upstream. -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
