Hi, Anurag Kumar Vulisha <anuragku@xxxxxxxxxx> writes: >>> The dma_map_sg() merges sg1 & sg2 memory regions into sg1- >>>dma_address. >>> Similarly sg3 & sg4 into sg2->dma_address, sg5 & sg6 into the >>> sg3->dma_address and sg6 & sg8 into sg4->dma_address. Here the >>memory >>> regions are merged but the page_link properties like SG_END are not >>> retained into the merged sgs. >> >>isn't this a bug in the scatterlist mapping code? Why doesn't it keep >>SG_END? >> > > Thanks for providing your comment. > > I don't think it is a bug, instead I feel some enhancement needs to be done in > dma-mapping code. > > SG_END represents the last sg entry in the sglist and it is correctly getting > set to the last sg entry. > > The issue happens only when 2 or more sg entry pages are merged into > contiguous dma-able address and sg_is_last() is used to find the last sg entry > with valid dma address. Right, and that's something that's bound to happen. I'm arguing that, perhaps, dma API should move SG_END in case entries are merged. > I think that along with sg_is_last() a new flag (SG_DMA_END) and function > (something like sg_dma_is_last() ) needs to be added into dma-mapping code for > identifying the last valid sg entry with valid dma address. So that we can > make use of that function instead of sg_is_last(). Sure, propose a patch to DMA API. -- balbi
Attachment:
signature.asc
Description: PGP signature
