Messages in this thread |  | | | Date | Thu, 21 May 2009 10:43:43 -0700 | | From | Jeremy Fitzhardinge <> | | Subject | Re: [PATCH V2 2/3] powerpc: Add support for swiotlb on 32-bit |
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Becky Bruce wrote: >> >> >> If we have something like in arch/{x86|ia64|powerpc}/dma-mapping.h: >> >> static inline int is_buffer_dma_capable(struct device *dev, >> dma_addr_t addr, size_t size) >> >> then we don't need two checking functions, address_needs_mapping and >> range_needs_mapping. > > It's never been clear to me *why* we had both in the first place - if > you can explain this, I'd be grateful :)
I was about to ask the same thing. It seems that range_needs_mapping should be able to do both jobs.
I think range_needs_mapping came from the Xen swiotlb changes, and address_needs_mapping came from your powerpc changes. Many of the changes were exact overlaps; I think this was one of the few instances where there was a difference.
We need a range check in Xen (rather than iterating over individual pages) because we want to check that the underlying pages are machine contiguous, but I think that's also sufficient to do whatever checks you need to do.
The other difference is that is_buffer_dma_capable operates on a dma_addr_t, which presumes that you can generate a dma address and then test for its validity. For Xen, it doesn't make much sense to talk about the dma_addr_t for memory which isn't actually dma-capable; we need the test to be in terms of phys_addr_t. Given that the two functions are always called from the same place, that doesn't seem to pose a problem.
So I think the unified function would be something like:
int range_needs_mapping(struct device *hwdev, phys_addr_t addr, size_t size);
which would be defined somewhere under asm/*.h. Would that work for powerpc? J
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