On Sun, Sep 25, 2016 at 1:02 AM, Greg Freemyer <greg.freemyer@xxxxxxxxx> wrote: > On Sat, Sep 24, 2016 at 9:33 AM, Muni Sekhar <munisekharrms@xxxxxxxxx> wrote: >> Hi All, >> >> I am working on a xilinx PCIe endpoint with DMA reference block. >> >> The DMA reference block design has 2 Scatter-Gather engines, one for >> each DMA channel. >> >> Channel 0 is for HostMemory -> DMA_REF FIFO transfers >> Channel 1 is for DMA_REF FIFO -> HostMemory transfers >> >> Each scatter-gather engine works through a linked list of Descriptors >> from which it generates the required DMA activity. >> >> >> The format of these descriptors is depicted as below: >> >> Offset @ 0x00 - LSBs of pointer to DMA data >> >> Offset @ 0x04 - MSBs of pointer to DMA data >> >> Offset @ 0x08 - Number of data bytes to be transferred. (note: only 8 >> byte aligned transfers supported) >> >> Offset @ 0x0C - LSBs of pointer to next Descriptor (Set this field & >> MSBs to zero to indicate end of descriptor list) >> >> Offset @ 0x10 - MSBs of pointer to next Descriptor >> >> >> >> Does the Linux kernel has any data structure to support the above >> mentioned scatter-gather descriptor? >> >> >> >> Will it be possible to use the kernel scatterlist API’s for this hardware? > > Muni, > > Have you checked that they don't have a pre-existing driver? > > http://www.wiki.xilinx.com/Linux+Drivers > > There are 5 different DMA drivers there. Assuming you have and the > DMA engine doesn't yet have a linux driver: > > I'm not sure I've ever written the low level scatter-gather DMA logic > for a DMA engine, but scatter-gather is decades old technology. > > The basic scatterlist is defined in: linux/scatterlist.h > > see http://lxr.free-electrons.com/source/include/linux/scatterlist.h#L10 > > === > 10 struct scatterlist { > 11 #ifdef CONFIG_DEBUG_SG > 12 unsigned long sg_magic; > 13 #endif > 14 unsigned long page_link; > 15 unsigned int offset; > 16 unsigned int length; > 17 dma_addr_t dma_address; > 18 #ifdef CONFIG_NEED_SG_DMA_LENGTH > 19 unsigned int dma_length; > 20 #endif > 21 }; > === > > The upper levels of the linux kernel will populate that and pass it > into the DMA engine driver. > > I believe your DMA engine driver will have to accept that scatterlist > coming from the upper layers of the kernel and map it to a new > structure to pass to your IOMMU. > Hi Greg, Thanks for the useful information, I will look at the existing xilinx DMA engine drivers and documentation for DMA-API's. > But don't trust my rather vague knowledge. Have you read: > > https://www.kernel.org/doc/Documentation/DMA-API.txt > https://www.kernel.org/doc/Documentation/DMA-API-HOWTO.txt > > Search through those for "scatter" and "sg". You will find the main > kernel structs and API. > > And of course, look at the existing xilinx DMA engine drivers and see > if there isn't one close to what you need. > > Hope that helps, > Greg -- Thanks, Sekhar _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
