[RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device memory management

On Mon, 19 Jul 2010 09:22:13 +0100
Russell King - ARM Linux [off-list ref] wrote:

quoted

If I want to share the buffer with another device I have to
make a copy of the entire thing then fix up the virtual mappings for
the other device I'm sharing with.

This is something the DMA API doesn't do - probably because there hasn't
been a requirement for it.

One of the issues for drivers is that by separating the mapped scatterlist
from the input buffer scatterlist, it creates something else for them to
allocate, which causes an additional failure point - and as all users sit
well with the current API, there's little reason to change especially
given the number of drivers which would need to be updated.

Agreed. There was the discussion about separating 'dma_addr and dma_len' from
scatterlist struct but I don't think that it's worth doing so.

I'm just proving that it's not as hard as you seem to be making out.

Agreed again.