iommu/dma: Refactor iommu_dma_alloc

Shuffle around the self-contained atomic and non-contiguous cases to
return early and get out of the way of the CMA case that we're about to
work on next.
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
[hch: slight changes to the code flow]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/dma-iommu.c

@@ -973,14 +973,19 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
 {
 	bool coherent = dev_is_dma_coherent(dev);
 	int ioprot = dma_info_to_prot(DMA_BIDIRECTIONAL, coherent, attrs);
+	pgprot_t prot = arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs);
 	size_t iosize = size;
+	struct page *page;
 	void *addr;
 
 	size = PAGE_ALIGN(size);
 	gfp |= __GFP_ZERO;
 
+	if (gfpflags_allow_blocking(gfp) &&
+	    !(attrs & DMA_ATTR_FORCE_CONTIGUOUS))
+		return iommu_dma_alloc_remap(dev, iosize, handle, gfp, attrs);
+
 	if (!gfpflags_allow_blocking(gfp)) {
-		struct page *page;
 		/*
 		 * In atomic context we can't remap anything, so we'll only
 		 * get the virtually contiguous buffer we need by way of a
@@ -1002,11 +1007,10 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
 				__free_pages(page, get_order(size));
 			else
 				dma_free_from_pool(addr, size);
-			addr = NULL;
+			return NULL;
+		}
+		return addr;
 	}
-	} else if (attrs & DMA_ATTR_FORCE_CONTIGUOUS) {
-		pgprot_t prot = arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs);
-		struct page *page;
 
 	page = dma_alloc_from_contiguous(dev, size >> PAGE_SHIFT,
 					 get_order(size), gfp & __GFP_NOWARN);
@@ -1014,27 +1018,23 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
 		return NULL;
 
 	*handle = __iommu_dma_map(dev, page_to_phys(page), iosize, ioprot);
-		if (*handle == DMA_MAPPING_ERROR) {
-			dma_release_from_contiguous(dev, page,
-						    size >> PAGE_SHIFT);
-			return NULL;
-		}
-		addr = dma_common_contiguous_remap(page, size, VM_USERMAP,
-						   prot,
+	if (*handle == DMA_MAPPING_ERROR)
+		goto out_free_pages;
+
+	addr = dma_common_contiguous_remap(page, size, VM_USERMAP, prot,
 			__builtin_return_address(0));
-		if (addr) {
+	if (!addr)
+		goto out_unmap;
+
 	if (!coherent)
 		arch_dma_prep_coherent(page, iosize);
 	memset(addr, 0, size);
-		} else {
-			__iommu_dma_unmap(dev, *handle, iosize);
-			dma_release_from_contiguous(dev, page,
-						    size >> PAGE_SHIFT);
-		}
-	} else {
-		addr = iommu_dma_alloc_remap(dev, iosize, handle, gfp, attrs);
-	}
 	return addr;
+out_unmap:
+	__iommu_dma_unmap(dev, *handle, iosize);
+out_free_pages:
+	dma_release_from_contiguous(dev, page, size >> PAGE_SHIFT);
+	return NULL;
 }
 
 static int __iommu_dma_mmap_pfn(struct vm_area_struct *vma,