[PATCH 2/8] PCI: Add pci_find_common_upstream_dev()

[Christoph Hellwig]

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.