On Mon, Mar 16, 2020 at 02:52:13AM -0700, Christoph Hellwig wrote: > On Mon, Mar 16, 2020 at 10:41:42AM +0100, Christian König wrote: > > Well I would prefer if the drivers can somehow express their requirements > > and get IOVA structures already in the form they need. > > > > Converting the IOVA data from one form to another is sometimes quite costly. > > Especially when it is only temporarily needed. > > We basically have two ways to generate the IOVA: > > - a linear translation for the direct mapping case or some dumb IOMMU > drivers - in that case case there is a 1:1 mapping between input > segments and output segments in DMA mapping > - a non-trivial IOMMU where all aligned segments are merged into > a single IOVA range > > So I don't really see how the dma layer could help much with any > limitation beyond existing max size and dma boundary ones. Christian are you thinking of something like the controllable address&flags scheme in hmm_range_fault() so that the dma_map process can write DMA address pages directly to some HW formatted structure? Jason
