On 26-03-2018 17:15, Robin Murphy wrote: > Hi Harsh, > > On 26/03/18 10:55, Harsh Jain wrote: >> Hi, >> >> Can we add offset to dma address received from IOMMU in scatter/Gather list >> before sending it to H/W. >> >> Address to HW = sg_dma_address(sg) + offset, where 0 < offset < >> sg_dma_len(sg). > > sg_dma_address() should already account for sg->offset (i.e. the start of the > buffer within the page. If there's a DMA API implementation failing to > respect that then that's a bug. Thanks. Here "offset" means size of last dma entry I had mapped to H/W structure. eg if dma length is 9K offset will be 0, 2K, 4K,6K,8K. > >> I need this operation to make sure our H/W does not receives entry of size >> greater than 2K. > > If however it's just that you want to fragment a single SG entry into > multiple commaneds/descriptors/etc. internally to your driver, then I can't > see that being an issue as long as you don't visibly modify the scatterlist > itself. If there's a genuine length and/or alignment limitation in the > hardware, though, it would be better to set up dev->dma_parms appropriately > to describe them, such that the subsystem responsible for generating the > scatterlist respects the appropriate constraints in the first place (and if > it doesn't, then that's another bug to fix). > Yes, I wants to fragment single entry into multiple such that it is less than 2K. eg. if sg->length == 5k , I will split into 3 entries addr1 = sg_dma_address(sg), len =2K addr2 = sg_dma_address(sg) + 2K, len = 2K addr3 = sg_dma_address(sg) +4K, len = 1K
> Robin. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
