iommu/dma: Remove bogus dma_supported() implementation

Back when this was first written, dma_supported() was somewhat of a
murky mess, with subtly different interpretations being relied upon in
various places. The "does device X support DMA to address range Y?"
uses assuming Y to be physical addresses, which motivated the current
iommu_dma_supported() implementation and are alluded to in the comment
therein, have since been cleaned up, leaving only the far less ambiguous
"can device X drive address bits Y" usage internal to DMA API mask
setting. As such, there is no reason to keep a slightly misleading
callback which does nothing but duplicate the current default behaviour;
we already constrain IOVA allocations to the iommu_domain aperture where
necessary, so let's leave DMA mask business to architecture-specific
code where it belongs.
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

arch/arm64/mm/dma-mapping.c

@@ -799,7 +799,6 @@ static struct dma_map_ops iommu_dma_ops = {
 	.sync_sg_for_device = __iommu_sync_sg_for_device,
 	.map_resource = iommu_dma_map_resource,
 	.unmap_resource = iommu_dma_unmap_resource,
-	.dma_supported = iommu_dma_supported,
 	.mapping_error = iommu_dma_mapping_error,
 };
 

drivers/iommu/dma-iommu.c

@@ -734,16 +734,6 @@ void iommu_dma_unmap_resource(struct device *dev, dma_addr_t handle,
 	__iommu_dma_unmap(iommu_get_domain_for_dev(dev), handle);
 }
 
-int iommu_dma_supported(struct device *dev, u64 mask)
-{
-	/*
-	 * 'Special' IOMMUs which don't have the same addressing capability
-	 * as the CPU will have to wait until we have some way to query that
-	 * before they'll be able to use this framework.
-	 */
-	return 1;
-}
-
 int iommu_dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
 {
 	return dma_addr == DMA_ERROR_CODE;

include/linux/dma-iommu.h

@@ -67,7 +67,6 @@ 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);
 void iommu_dma_unmap_resource(struct device *dev, dma_addr_t handle,
 		size_t size, enum dma_data_direction dir, unsigned long attrs);
-int iommu_dma_supported(struct device *dev, u64 mask);
 int iommu_dma_mapping_error(struct device *dev, dma_addr_t dma_addr);
 
 /* The DMA API isn't _quite_ the whole story, though... */