On Fri, Nov 16, 2018 at 08:52:14AM -0800, Palmer Dabbelt wrote: > As far as I can tell, it looks like m68k, mips, and powerpc mention an > IOMMU in their ports, don't set ARCH_HAS_SG_CHAIN, and with this patch set > won't set ARCH_NO_SG_CHAIN. m68k has no iommu, and not operations that operate on a scatterlist. mips has a trivial iommu driver (jazzdma), but I wrote the current instance of it, nad it is fine. powerpc has various iommu, but actually enables ARCH_HAS_SG_CHAIN unconditionally. > The issue is that I'm not sure how to > determine what constitutes a horrible legacy IOMMU, at least with respect > to not being able to use scatterlist chaining. It basically means someone is iterating using manual pointer arithmetics over a multi-element scatterlist instead of using the sg_next and for_each_sg helpers.
