dma_alloc_pages / dma_alloc_noncoherent fixups

[Christoph Hellwig]

Hi all,

this series has a bunch of fixups for the noncoherent DMA allocator
rework that recently landed in linux-next.

I think the most important part is that the idea of vmap()ing
non-contiguous allocations in dma_alloc_noncoherent doesn't work very
well after all.  It means we can't just rely on virt_to_page to get
the page and just use remap_pfn_range or stuff it into other APIs,
but on the other hand it also isn't really generic enought for what
the media APIs seems to want.

So the first patch reverts that change, and the last patch suggests
a different lower level API which should allow the media code to do
all it wants.

I'd suggest all but the last patch for the current merge window, and
we should have a discussion on how well the last one suits the media
subsystem, and probably merge it together with any media changes to
use the required API.