AMD IOMMU: avoid unnecessary low zone allocation in alloc_coherent

x86's common alloc_coherent (dma_alloc_coherent in dma-mapping.h) sets
up the gfp flag according to the device dma_mask but AMD IOMMU doesn't
need it for devices that the IOMMU can do virtual mappings for. This
patch avoids unnecessary low zone allocation.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/amd_iommu.c

@@ -1173,6 +1173,9 @@ static void *alloc_coherent(struct device *dev, size_t size,
 	if (!check_device(dev))
 		return NULL;
 
+	if (!get_device_resources(dev, &iommu, &domain, &devid))
+		flag &= ~(__GFP_DMA | __GFP_HIGHMEM | __GFP_DMA32);
+
 	virt_addr = (void *)__get_free_pages(flag, get_order(size));
 	if (!virt_addr)
 		return 0;
@@ -1180,8 +1183,6 @@ static void *alloc_coherent(struct device *dev, size_t size,
 	memset(virt_addr, 0, size);
 	paddr = virt_to_phys(virt_addr);
 
-	get_device_resources(dev, &iommu, &domain, &devid);
-
 	if (!iommu || !domain) {
 		*dma_addr = (dma_addr_t)paddr;
 		return virt_addr;