Re: [PATCH v4 9/9] x86: convert dma_map_ops to support mapping a __pfn_t.

[Christoph Hellwig]

On Fri, Jun 05, 2015 at 05:19:55PM -0400, Dan Williams wrote:
> As long as a dma_map_sg() implementation avoids sg_page() conversions it
> can support scatterlists that carry "page-less" __pfn_t entries.
> However, a couple implementations require that __pfn_t_has_page() is
> always true. The Xen swiotlb implementation's entanglements with ARM and
> the Calgary MMUs requirement to have a pre-existing virtual mapping make
> them unable to support this conversion (i.e. these now have 'depends on
> !HAVE_DMA_PFN').

That's why we really need a whole kernel conversion and not just a piecemail
one.  Given how trivial this patch is that doesn't look like a too big
task ayway.
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