DMA mapping API(IOMMU) for ARM64?

[Will Deacon]

On Tue, Jun 18, 2013 at 03:39:55AM +0100, Hiroshi Doyu wrote:
> Hi,

Hello Hiroshi,

> Currently ARM64 supports swiotlb only as below[1]. AFAIU, swiotlb
> provides some kind of bounce buffer for some restricted H/Ws, and it
> cannot replace IOMMU H/W completely. So I'm wondering that we would
> need the IOMMU versions of dma_map_ops as Marek did for ARM32. If my
> understanding is correct, do you guys have any idea how it's going to
> be implemented? Can we reuse the current version of "iommu_ops" in
> "arch/arm/mm/dma-mapping.c" for ARM64 as well? Or do we need to
> rewrite 64bit version of iommu_ops completely in the same file as one
> with swiotlb, "arch/arm64/mm/dma-mapping.c"?
> 
> Any feedback would be really appreciated.

I've spoken briefly with Catalin about this and it seems like there might be
*some* scope for sharing common dma-mapping code between architectures.
There doesn't really need to be any architecture-specific details in
allocating iova space and the interface to the iommu drivers is
well-defined. The arch-specific stuff is bogged down in the non-coherent
buffer management, but that doesn't necessarily equate to lots of code.

So, the best bet would be to figure out how to split up what we have under
arch/arm/ so that it can be re-used by arm64 and potentially other
architectures (powerpc has some simple stuff for coherent mappings and some
less-simple stuff for non-coherent buffers).

Will