[PATCH 1/2] arm64: dma-mapping: implement dma_get_sgtable()
robin.murphy at arm.com
Mon Jul 20 10:00:57 PDT 2015
On 20/07/15 17:36, Will Deacon wrote:
> On Fri, Jul 17, 2015 at 04:58:21PM +0100, Robin Murphy wrote:
>> The default dma_common_get_sgtable() implementation relies on the CPU
>> address of the buffer being a regular lowmem address. This is not always
>> the case on arm64, since allocations from the various DMA pools may have
>> remapped vmalloc addresses, rendering the use of virt_to_page() invalid.
>> Fix this by providing our own implementation based on the fact that we
>> can safely derive a physical address from the DMA address in both cases.
>> CC: Jon Medhurst <tixy at linaro.org>
>> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
>> arch/arm64/mm/dma-mapping.c | 14 ++++++++++++++
>> 1 file changed, 14 insertions(+)
>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
>> index d16a1ce..4b9b600 100644
>> --- a/arch/arm64/mm/dma-mapping.c
>> +++ b/arch/arm64/mm/dma-mapping.c
>> @@ -337,10 +337,24 @@ static int __swiotlb_mmap(struct device *dev,
>> return __dma_common_mmap(dev, vma, cpu_addr, dma_addr, size);
>> +int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt,
>> + void *cpu_addr, dma_addr_t handle, size_t size,
>> + struct dma_attrs *attrs)
>> + int ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
>> + if (!ret)
>> + sg_set_page(sgt->sgl, phys_to_page(dma_to_phys(dev, handle)),
>> + PAGE_ALIGN(size), 0);
>> + return ret;
> Any reason not to do this in dma_common_get_sgtable?
Summarising the discussion over at , most architectures seem to
depend on dma_common_get_sgtable, but only a handful implement
dma_to_phys (plus this approach seems to match the original intent).
There doesn't seem to be a nice solution for doing this in common code
without a big cross-architecture patch, and it's somewhat questionable
how widely this is actually needed.
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