dma-mapping: call ->unmap_page and ->unmap_sg unconditionally

Almost all instances of the dma_map_ops ->map_page()/map_sg() methods
implement ->unmap_page()/unmap_sg() too.  The once instance which doesn't
dma_dummy_ops which is used to fail the DMA mapping and thus there won't
be any calls to ->unmap_page()/unmap_sg().

Remove the checks for ->unmap_page()/unmap_sg() and call them directly to
create an interface that is symmetrical to ->map_page()/map_sg().
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/dummy.c

@@ -17,6 +17,15 @@ static dma_addr_t dma_dummy_map_page(struct device *dev, struct page *page,
 {
 	return DMA_MAPPING_ERROR;
 }
+static void dma_dummy_unmap_page(struct device *dev, dma_addr_t dma_handle,
+		size_t size, enum dma_data_direction dir, unsigned long attrs)
+{
+	/*
+	 * Dummy ops doesn't support map_page, so unmap_page should never be
+	 * called.
+	 */
+	WARN_ON_ONCE(true);
+}
 
 static int dma_dummy_map_sg(struct device *dev, struct scatterlist *sgl,
 		int nelems, enum dma_data_direction dir,
@@ -25,6 +34,16 @@ static int dma_dummy_map_sg(struct device *dev, struct scatterlist *sgl,
 	return -EINVAL;
 }
 
+static void dma_dummy_unmap_sg(struct device *dev, struct scatterlist *sgl,
+		int nelems, enum dma_data_direction dir,
+		unsigned long attrs)
+{
+	/*
+	 * Dummy ops doesn't support map_sg, so unmap_sg should never be called.
+	 */
+	WARN_ON_ONCE(true);
+}
+
 static int dma_dummy_supported(struct device *hwdev, u64 mask)
 {
 	return 0;
@@ -33,6 +52,8 @@ static int dma_dummy_supported(struct device *hwdev, u64 mask)
 const struct dma_map_ops dma_dummy_ops = {
 	.mmap                   = dma_dummy_mmap,
 	.map_page               = dma_dummy_map_page,
+	.unmap_page             = dma_dummy_unmap_page,
 	.map_sg                 = dma_dummy_map_sg,
+	.unmap_sg               = dma_dummy_unmap_sg,
 	.dma_supported          = dma_dummy_supported,
 };

kernel/dma/mapping.c

@@ -177,7 +177,7 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size,
 	if (dma_map_direct(dev, ops) ||
 	    arch_dma_unmap_page_direct(dev, addr + size))
 		dma_direct_unmap_page(dev, addr, size, dir, attrs);
-	else if (ops->unmap_page)
+	else
 		ops->unmap_page(dev, addr, size, dir, attrs);
 	debug_dma_unmap_page(dev, addr, size, dir);
 }
@@ -291,7 +291,7 @@ void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
 	if (dma_map_direct(dev, ops) ||
 	    arch_dma_unmap_sg_direct(dev, sg, nents))
 		dma_direct_unmap_sg(dev, sg, nents, dir, attrs);
-	else if (ops->unmap_sg)
+	else
 		ops->unmap_sg(dev, sg, nents, dir, attrs);
 }
 EXPORT_SYMBOL(dma_unmap_sg_attrs);