Messages in this thread | | | Date | Mon, 29 Jun 2015 11:37:37 +0100 | From | Catalin Marinas <> | Subject | Re: [RFC PATCH v3] arm DMA: Fix allocation from CMA for coherent DMA |
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On Sun, Jun 28, 2015 at 10:14:43PM +0200, Lorenzo Nava wrote: > On Fri, Jun 26, 2015 at 6:25 PM, Catalin Marinas > <catalin.marinas@arm.com> wrote: > > On Thu, Jun 18, 2015 at 11:44:22PM +0200, Lorenzo Nava wrote: > >> @@ -680,9 +694,14 @@ void *arm_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle, > >> static void *arm_coherent_dma_alloc(struct device *dev, size_t size, > >> dma_addr_t *handle, gfp_t gfp, struct dma_attrs *attrs) > >> { > >> - pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL); > >> + pgprot_t prot; > >> void *memory; > >> > >> + if (attrs == NULL) > >> + prot = PAGE_KERNEL; > >> + else > >> + prot = __get_dma_pgprot(attrs, PAGE_KERNEL); > >> + > >> if (dma_alloc_from_coherent(dev, size, handle, &memory)) > >> return memory; > > > > I still think this is the wrong way to fix. It doesn't address the > > coherent dma mmap operation. I already replied on the previous version > > that we should rather have an extra argument "coherent" to > > __get_dma_pgprot(). > > I avoided touching the __get_dma_pgprot() function because it affects > a lot of different functions. > If you think that the implementation you suggested in previous reply > was ok and doesn't introduce problems on the other functions using the > __get_dma_pgprot(), for me it's of course ok as well.
I forgot about the arm_dma_mmap fix here:
https://lkml.org/lkml/2015/5/7/512
So we either fix both cases by changing __get_dma_pgprot() or just go for Mike's and your patches as above. It's up to Russell.
At some point, we could do with some more clean-up in the dma-mapping.c. For example, both __alloc_simple_buffer() and __alloc_from_contiguous() end up calling __dma_clear_buffer() even when not necessary (cacheable mapping). Not too bad though as this is only done when setting up the buffer.
> Do you see any code that maybe need a double check: I'm thinking, for > example, at the function arm_iommu_alloc_attrs() and > arm_iommu_mmap_attrs()?
I think this has bigger problems. The code seems to only be right for non-cacheable mappings. For cacheable/coherent iommu mappings, I don't see any use of the IOMMU_CACHE attribute (should it be returned by __dma_direction_to_prot?).
-- Catalin
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