Messages in this thread | | | Date | Tue, 11 Jul 2017 16:19:37 +0200 | From | Christoph Hellwig <> | Subject | Re: [PATCH v2 1/2] drivers: dma-coherent: Fix dev->cma_area vs dev->dma_mem breakage |
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On Fri, Jul 07, 2017 at 05:06:52PM +0100, Robin Murphy wrote: > I don't think we need to go that far, I reckon it would be clear enough > to just split the per-device vs. global pool interfaces, something like > I've sketched out below (such that the ops->alloc implementation calls > dma_alloc_from_global_coherent() if dma_alloc_from_contiguous() fails). > > If anyone wants to take that and run with it, feel free.
I like this basic idea. It also fits into one of my plans for the 4.14 merge window - I want to enhance the lib/dma-noop.c so that it can use different allocators and mapping helpers, e.g. for the allocators what makes sense is:
(1) simple page allocator (as-is) (2) CMA (3) swiotlb (4) the OF coherent allocator from your draft patch
and then for the mapping into phys space we can use
(1) virto_to_phys (as-is) (2) arch helper (e.g. like done in mips plat support) (3) maybe some common form of ioremap / vmap instead of various duplicates
With that we should be able to cosolidate most direct mapped dma_ops for architectures that do not require cache flushing into common code. As a next step we could think about useful cache flushing hooks.
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