Dan Williams started to look into addressing I/O to and from Persistent Memory in his series from June: http://thread.gmane.org/gmane.linux.kernel.cross-arch/27944 I've started looking into DMA mapping of these SGLs specifically instead of the map_pfn method in there. In addition to supporting NVDIMM backed I/O I also suspect this would be highly useful for media drivers that go through nasty hoops to be able to DMA from/to their ioremapped regions, with vb2_dc_get_userptr in drivers/media/v4l2-core/videobuf2-dma-contig.c being a prime example for the unsafe hacks currently used. It turns out most DMA mapping implementation can handle SGLs without page structures with some fairly simple mechanical work. Most of it is just about consistently using sg_phys. For implementations that need to flush caches we need a new helper that skips these cache flushes if a entry doesn't have a kernel virtual address. However the ccio (parisc) and sba_iommu (parisc & ia64) IOMMUs seem to be operate mostly on virtual addresses. It's a fairly odd concept that I don't fully grasp, so I'll need some help with those if we want to bring this forward. Additional this series skips ARM entirely for now. The reason is that most arm implementations of the .map_sg operation just iterate over all entries and call ->map_page for it, which means we'd need to convert those to a ->map_pfn similar to Dan's previous approach. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
