On Thu, Mar 29, 2018 at 09:58:54PM -0400, Jerome Glisse wrote:

dma_map_resource() is the right API (thought its current implementation is fill with x86 assumptions). So i would argue that arch can decide to implement it or simply return dma error address which trigger fallback path into the caller (at least for GPU drivers). SG variant can be added on top.

It isn't in general. It doesn't integrate with scatterlists (see my comment to page one), and it doesn't integrate with all the subsystems that also need a kernel virtual address.