On Sat, Oct 13, 2018 at 11:01 PM, Liam Mark <lmark@xxxxxxxxxxxxxx> wrote: > On Fri, 12 Oct 2018, Laura Abbott wrote: >> I thought there might have been some Qualcomm >> stuff that did that (Liam? Todd?) > > Yes we have a form of "lazy mapping", which clients can opt into using, > which results in iommu page table mapping not being unmaped on dma-unamp. > Instead they are unmapped when the buffer is destroyed. > > It is important to note that in our "lazy mapping" implementation cache > maintenance is still applied on dma-map and dma-unmap. > If you need a full description of this feature I can provide it. > >> >> I suspect most of the cost of the dma_map/dma_unmap is from the >> cache flushing and not the actual mapping operations. If this >> is the case, another option might be to figure out how to >> incorporate dma_attrs so drivers can use DMA_ATTR_SKIP_CPU_SYNC >> to decide when they actually want to sync. > > We have support for this locally on our 4.14 branch. > > We have added a dma_map_attrs field to the dma_buf_attachment struct, > clients can then specify dma-attributes here such as > DMA_ATTR_SKIP_CPU_SYNC before dma-mapping the buffer, then we ensure that > these dma attributes are passed to dma_map_sg_attrs when ion_map_dma_buf > is called (same for ion_unmap_dma_buf). Do you happen to have a pointer to the tree if its public? thanks -john _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
