Hello,
On 6/18/2013 2:50 PM, Catalin Marinas wrote:
On Tue, Jun 18, 2013 at 12:01:37PM +0100, Hiroshi Doyu wrote:
Arnd Bergmann arnd@arndb.de wrote @ Tue, 18 Jun 2013 12:32:44 +0200:
On Tuesday 18 June 2013 11:19:14 Will Deacon wrote:
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).
I'm sure that other architectures are interested in sharing the code. Best move it into the global mm/ directory, at least the version for coherent mappings.
I'm guessing that this kind of unification usually takes some time since we need to factor out the common code from the different ${ARCH}/mm/dma-mapping.c. Also some of ${ARCH} has IOMMU support in it. So if we want to develop our 64-bit ARM with working DMA mapping API during this transition, the step to take would be:
1, Copy arch/arm/mm/dma-mapping.c arch/arm64/mm/dma-mapping.c(+swiotlb) 2, Adapt arch/arm64/mm/dma-mapping.c(+swiotlb) to 64bit compatible. 3, Factor out the common code from them into mm/dma-mapping.c
Or add the relevant code to something like lib/iommu-helper.c, convert arm64 to use that and we can work on converting arm and other architectures afterwards.
I think that this would be the best way of providing iommu support for dma mapping subsystem(s). I initially put it in arm/mm/dma-mapping.c because it was the first approach of integrating generic IOMMU with DMA-mapping and it was simply easier to have all the code in one place. Now, when second client of such approach comes, it should be much easier to identify which part of the code is common and which one is specific to particular implementation. Feel free to ask any questions if you need help. I don't have access to any ARM64 machine or simulator, so I can only review the code.
Best regards