Messages in this thread | | | Date | Tue, 30 Apr 2019 12:46:13 -0700 | From | Nicolin Chen <> | Subject | Re: [RFC/RFT PATCH 1/2] dma-contiguous: Simplify dma_*_from_contiguous() function calls |
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On Tue, Apr 30, 2019 at 05:18:33PM +0200, Christoph Hellwig wrote: > On Tue, Apr 30, 2019 at 01:37:54PM +0100, Robin Murphy wrote: > > On 30/04/2019 11:56, Christoph Hellwig wrote: > >> So while I really, really like this cleanup it turns out it isn't > >> actually safe for arm :( arm remaps the CMA allocation in place > >> instead of using a new mapping, which can be done because they don't > >> share PMDs with the kernel. > >> > >> So we'll probably need a __dma_alloc_from_contiguous version with > >> an additional bool fallback argument - everyone but arms uses > >> dma_alloc_from_contiguous as in your patch, just arm will get the > >> non-fallback one. > > > > Or we even just implement dma_{alloc,free}_contiguous() as a wrapper around > > the existing APIs so that users can be thoroughly checked and converted > > one-by-one. > > Yeah. Actually given all the contention I wonder if the easiest solution > for now is to just open code the cma_alloc/cma_free calls in dma-direct > and dma-iommu, with the hopes that everyone is going to migrate to those > implementations in the mid-term anyway and dma_alloc_from_contiguous / > dma_release_from_contiguous just go away..
Thanks for the comments.
Listing all the solutions as a summary: A) Add "bool fallback" to dma_{alloc,free}_contiguous, and let ARM use fallback=false. B) Continue replacing "_from" with dma_{alloc,free}_contiguous but let callers like ARM use cma_alloc/free() directly. C) Have both new dma_{alloc,free}_contiguous and "_from" funcs. Implement the new one to dma-direct only as an initial step and change others one-by-one in the future.
Combining the comments at alloc_pages_node(), I guess that the Solution C would be a better (cleaner) one?
List of to-change callers for Solution C: kernel/dma/direct.c
List of to-exclude-for-now callers for Solution C: arch/arm64/mm/dma-mapping.c drivers/iommu/amd_iommu.c drivers/iommu/intel-iommu.c arch/arm/mm/dma-mapping.c arch/xtensa/kernel/pci-dma.c kernel/dma/remap.c
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