On Tue, Jan 10, 2017 at 11:47:42AM +0100, Arnd Bergmann wrote: > I see that we have CONFIG_ARCH_PHYS_ADDR_T_64BIT on a couple of > 32-bit architectures without swiotlb (arc, arm, some mips32), and > there are several 64-bit architectures that do not have swiotlb > (alpha, parisc, s390, sparc). I believe that alpha, s390 and sparc > always use some form of IOMMU, but the other four apparently don't, > so we would need to add swiotlb support there to remove all the > bounce buffering in network and block layers.
mips has lots of weird swiotlb wire-up in it's board code (the swiotlb arch glue really needs some major cleanup..), as does arm. Not sure about the others. Getting rid of highmem bouncing in the block layer will take some time as various PIO-only drivers rely on it at the moment. These should all be convertable to kmap that data, but it needs a careful audit first. For 4.11 I'll plan to switch away from bouncing highmem by default at least, though and maybe also convert a few PIO drivers.
