[PATCH v2 1/2] iommu/dma: Implement dma_{map,unmap}_resource()

[Robin Murphy]

On 10/11/16 12:24, Joerg Roedel wrote:
> On Wed, Oct 26, 2016 at 06:43:56PM +0100, Robin Murphy wrote:
>> With the new dma_{map,unmap}_resource() functions added to the DMA API
>> for the benefit of cases like slave DMA, add suitable implementations to
>> the arsenal of our generic layer. Since cache maintenance should not be
>> a concern, these can both be standalone callback implementations without
>> the need for arch code wrappers.
>>
>> CC: Joerg Roedel <joro at 8bytes.org>
>> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
>> ---
>>
>> v2: Use iommu_dma_unmap_page for symmetry, instead of being sneaky.
>>
>>  drivers/iommu/dma-iommu.c | 13 +++++++++++++
>>  include/linux/dma-iommu.h |  4 ++++
>>  2 files changed, 17 insertions(+)
>>
>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>> index c5ab8667e6f2..a2fd90a6a782 100644
>> --- a/drivers/iommu/dma-iommu.c
>> +++ b/drivers/iommu/dma-iommu.c
>> @@ -624,6 +624,19 @@ void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg, int nents,
>>  	__iommu_dma_unmap(iommu_get_domain_for_dev(dev), sg_dma_address(sg));
>>  }
>>  
>> +dma_addr_t iommu_dma_map_resource(struct device *dev, phys_addr_t phys,
>> +		size_t size, enum dma_data_direction dir, unsigned long attrs)
>> +{
>> +	return iommu_dma_map_page(dev, phys_to_page(phys), offset_in_page(phys),
>> +			size, dma_direction_to_prot(dir, false) | IOMMU_MMIO);
>> +}
> 
> Isn't the whole point of map_resource that we can map regions which have
> no 'struct page' associated? The use phys_to_page() will certainly not
> do the right thing here.

Perhaps it's a bit cheeky, but the struct page pointer is never
dereferenced - the only thing iommu_dma_map_page() does with it is
immediately convert it back again. Is there ever a case where
page_to_phys(phys_to_page(phys)) != phys ?

Robin.