Re: [PATCH 5/9] PCI: host: brcmstb: add dma-ranges for inbound traffic

[Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>]

On Tue, Oct 17, 2017 at 12:11:55PM -0400, Jim Quinlan wrote:
> My understanding is that dma_pfn_offset is that it is a single
> constant offset from RAM, in our case, to map to PCIe space.

Yes.

> But in
> my commit message I detail how our PCIe controller presents memory
> with multiple regions with multiple different offsets. If an EP device
> maps to a region on the host memory, yes we can set the dma_pfn_offset
> for that device for that location within that range,.  But if the
> device then unmaps and allocates from another region with a different
> offset, it won't work.  If  I set dma_pfn_offset I have to assume that
> the device is using only one region of memory only, not more than one,
> and that it is not unmapping that region and mapping another (with a
> different offset).  Can I make those assumptions?

No, we can't make that assumption unfortunately.  But how is your
code going to work if the mapping spans multiple of your translation
regions?

Also I really don't think the stacking of dma_ops as in this patch
is a good idea.  For MIPS you should do the variant suggested in
the patch description and hook into dma_to_phys/phys_to_dma helpers,
and for ARM/ARM64 you should talk to the maintainers on how they
want the translation integrated.