dma-iommu: refactor iommu_dma_alloc_remap

Split out a new helper that only allocates a sg_table worth of
memory without mapping it into contiguous kernel address space.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Tested-by: Ricardo Ribalda <ribalda@chromium.org>

drivers/iommu/dma-iommu.c

@@ -650,23 +650,12 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev,
 	return pages;
 }
 
-/**
- * iommu_dma_alloc_remap - Allocate and map a buffer contiguous in IOVA space
- * @dev: Device to allocate memory for. Must be a real device
- *	 attached to an iommu_dma_domain
- * @size: Size of buffer in bytes
- * @dma_handle: Out argument for allocated DMA handle
- * @gfp: Allocation flags
- * @prot: pgprot_t to use for the remapped mapping
- * @attrs: DMA attributes for this allocation
- *
- * If @size is less than PAGE_SIZE, then a full CPU page will be allocated,
+/*
+ * If size is less than PAGE_SIZE, then a full CPU page will be allocated,
  * but an IOMMU which supports smaller pages might not map the whole thing.
- *
- * Return: Mapped virtual address, or NULL on failure.
  */
-static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
-		dma_addr_t *dma_handle, gfp_t gfp, pgprot_t prot,
+static struct page **__iommu_dma_alloc_noncontiguous(struct device *dev,
+		size_t size, struct sg_table *sgt, gfp_t gfp, pgprot_t prot,
 		unsigned long attrs)
 {
 	struct iommu_domain *domain = iommu_get_dma_domain(dev);
@@ -676,11 +665,7 @@ static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
 	int ioprot = dma_info_to_prot(DMA_BIDIRECTIONAL, coherent, attrs);
 	unsigned int count, min_size, alloc_sizes = domain->pgsize_bitmap;
 	struct page **pages;
-	struct sg_table sgt;
 	dma_addr_t iova;
-	void *vaddr;
-
-	*dma_handle = DMA_MAPPING_ERROR;
 
 	if (static_branch_unlikely(&iommu_deferred_attach_enabled) &&
 	    iommu_deferred_attach(dev, domain))
@@ -707,38 +692,56 @@ static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
 	if (!iova)
 		goto out_free_pages;
 
-	if (sg_alloc_table_from_pages(&sgt, pages, count, 0, size, GFP_KERNEL))
+	if (sg_alloc_table_from_pages(sgt, pages, count, 0, size, GFP_KERNEL))
 		goto out_free_iova;
 
 	if (!(ioprot & IOMMU_CACHE)) {
 		struct scatterlist *sg;
 		int i;
 
-		for_each_sg(sgt.sgl, sg, sgt.orig_nents, i)
+		for_each_sg(sgt->sgl, sg, sgt->orig_nents, i)
 			arch_dma_prep_coherent(sg_page(sg), sg->length);
 	}
 
-	if (iommu_map_sg_atomic(domain, iova, sgt.sgl, sgt.orig_nents, ioprot)
+	if (iommu_map_sg_atomic(domain, iova, sgt->sgl, sgt->orig_nents, ioprot)
 			< size)
 		goto out_free_sg;
 
+	sgt->sgl->dma_address = iova;
+	return pages;
+
+out_free_sg:
+	sg_free_table(sgt);
+out_free_iova:
+	iommu_dma_free_iova(cookie, iova, size, NULL);
+out_free_pages:
+	__iommu_dma_free_pages(pages, count);
+	return NULL;
+}
+
+static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
+		dma_addr_t *dma_handle, gfp_t gfp, pgprot_t prot,
+		unsigned long attrs)
+{
+	struct page **pages;
+	struct sg_table sgt;
+	void *vaddr;
+
+	pages = __iommu_dma_alloc_noncontiguous(dev, size, &sgt, gfp, prot,
+						attrs);
+	if (!pages)
+		return NULL;
+	*dma_handle = sgt.sgl->dma_address;
+	sg_free_table(&sgt);
 	vaddr = dma_common_pages_remap(pages, size, prot,
 			__builtin_return_address(0));
 	if (!vaddr)
 		goto out_unmap;
-
-	*dma_handle = iova;
-	sg_free_table(&sgt);
 	return vaddr;
 
 out_unmap:
-	__iommu_dma_unmap(dev, iova, size);
-out_free_sg:
-	sg_free_table(&sgt);
-out_free_iova:
-	iommu_dma_free_iova(cookie, iova, size, NULL);
-out_free_pages:
-	__iommu_dma_free_pages(pages, count);
+	__iommu_dma_unmap(dev, *dma_handle, size);
+	__iommu_dma_free_pages(pages, PAGE_ALIGN(size) >> PAGE_SHIFT);
 	return NULL;
 }