[PATCH v4] arm DMA: Fix allocation from CMA for coherent DMA
catalin.marinas at arm.com
Tue Jun 30 04:05:22 PDT 2015
On Mon, Jun 29, 2015 at 07:10:45PM +0200, Lorenzo Nava wrote:
> This patch allows the use of CMA for DMA coherent memory allocation.
> At the moment if the input parameter "is_coherent" is set to true
> the allocation is not made using the CMA, which I think is not the
> desired behaviour.
> Signed-off-by: Lorenzo Nava <lorenx4 at xxxxxxxx>
It's nice to have a proper email address here.
> @@ -680,9 +684,14 @@ 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;
We have a slight inconsistency with commit 55af8a91640d (ARM: 8387/1:
arm/mm/dma-mapping.c: Add arm_coherent_dma_mmap) where the attrs are not
honoured for the coherent ops. That is, DMA_ATTRS_WRITE_COMBINE
doesn't have any effect for mmap but with your patch it still has an
effect on alloc.
I think we could just ignore it, the WRITE_COMBINE attr is a hint that
the arch may or may not implement and I haven't seen it used with
coherent mappings. So in this case just pass PAGE_KERNEL to
__dma_alloc() directly without calling __get_dma_pgprot().
(it also looks like commit 55af8a91640d left an unused attrs argument
for __arm_dma_mmap that can be removed as well)
Apart from the above, you can add:
Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
More information about the linux-arm-kernel