+static void *loongson_dma_alloc_coherent(struct device *dev, size_t size,
+				dma_addr_t *dma_handle, gfp_t gfp, struct dma_attrs *attrs)
+{
+	void *ret;
+
+	if (dma_alloc_from_coherent(dev, size, dma_handle, &ret))
+		return ret;
+
+	/* ignore region specifiers */
+	gfp &= ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM);
+
+#ifdef CONFIG_ZONE_DMA
+	if (dev == NULL)
+		gfp |= __GFP_DMA;

When would this happen? dev == NULL?

+	else if (dev->coherent_dma_mask <= DMA_BIT_MASK(24))
+		gfp |= __GFP_DMA;
+	else
+#endif
+#ifdef CONFIG_ZONE_DMA32
+	if (dev->coherent_dma_mask <= DMA_BIT_MASK(32))
+		gfp |= __GFP_DMA32;
+	else

Why the 'else'

+#endif
+	;

why?

+	gfp |= __GFP_NORETRY;
+
+	ret = swiotlb_alloc_coherent(dev, size, dma_handle, gfp);
+	mb();

Why the 'mb()' ? Can you just do
	return swiotlb_alloc_coherent(...) 

+	return ret;
+}
+
+static void loongson_dma_free_coherent(struct device *dev, size_t size,
+				void *vaddr, dma_addr_t dma_handle, struct dma_attrs *attrs)
+{
+	int order = get_order(size);
+
+	if (dma_release_from_coherent(dev, order, vaddr))
+		return;
+
+	swiotlb_free_coherent(dev, size, vaddr, dma_handle);
+}
+
+static dma_addr_t loongson_dma_map_page(struct device *dev, struct page *page,
+				unsigned long offset, size_t size,
+				enum dma_data_direction dir,
+				struct dma_attrs *attrs)
+{
+	dma_addr_t daddr = swiotlb_map_page(dev, page, offset, size,
+					dir, attrs);
+	mb();

Please do 'return swiotlb_map_page(..)'..

But if you are doing that why don't you just set the dma_ops.map_page = swiotlb_map_page
?

+	return daddr;
+}
+
+static int loongson_dma_map_sg(struct device *dev, struct scatterlist *sg,
+				int nents, enum dma_data_direction dir,
+				struct dma_attrs *attrs)
+{
+	int r = swiotlb_map_sg_attrs(dev, sg, nents, dir, NULL);
+	mb();
+
+	return r;
+}
+
+static void loongson_dma_sync_single_for_device(struct device *dev,
+				dma_addr_t dma_handle, size_t size,
+				enum dma_data_direction dir)
+{
+	swiotlb_sync_single_for_device(dev, dma_handle, size, dir);
+	mb();
+}
+
+static void loongson_dma_sync_sg_for_device(struct device *dev,
+				struct scatterlist *sg, int nents,
+				enum dma_data_direction dir)
+{
+	swiotlb_sync_sg_for_device(dev, sg, nents, dir);
+	mb();
+}
+

I am not really sure why you have these extra functions, when you could
just modify the dma_ops to point to the swiotlb ones

+static dma_addr_t loongson_unity_phys_to_dma(struct device *dev, phys_addr_t paddr)
+{
+	return (paddr < 0x10000000) ?
+			(paddr | 0x0000000080000000) : paddr;
+}
+
+static phys_addr_t loongson_unity_dma_to_phys(struct device *dev, dma_addr_t daddr)
+{
+	return (daddr < 0x90000000 && daddr >= 0x80000000) ?
+			(daddr & 0x0fffffff) : daddr;
+}
+
+struct loongson_dma_map_ops {
+	struct dma_map_ops dma_map_ops;
+	dma_addr_t (*phys_to_dma)(struct device *dev, phys_addr_t paddr);
+	phys_addr_t (*dma_to_phys)(struct device *dev, dma_addr_t daddr);
+};
+
+dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr)
+{
+	struct loongson_dma_map_ops *ops = container_of(get_dma_ops(dev),
+					struct loongson_dma_map_ops, dma_map_ops);
+
+	return ops->phys_to_dma(dev, paddr);
+}
+
+phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr)
+{
+	struct loongson_dma_map_ops *ops = container_of(get_dma_ops(dev),
+					struct loongson_dma_map_ops, dma_map_ops);
+
+	return ops->dma_to_phys(dev, daddr);
+}
+
+static int loongson_dma_set_mask(struct device *dev, u64 mask)
+{
+	/* Loongson doesn't support DMA above 32-bit */
+	if (mask > DMA_BIT_MASK(32))
+		return -EIO;
+
+	*dev->dma_mask = mask;
+
+	return 0;
+}
+
+static struct loongson_dma_map_ops loongson_linear_dma_map_ops = {
+	.dma_map_ops = {
+		.alloc = loongson_dma_alloc_coherent,
+		.free = loongson_dma_free_coherent,
+		.map_page = loongson_dma_map_page,

But why not 'swiotlb_map_page'?

+		.unmap_page = swiotlb_unmap_page,
+		.map_sg = loongson_dma_map_sg,
+		.unmap_sg = swiotlb_unmap_sg_attrs,
+		.sync_single_for_cpu = swiotlb_sync_single_for_cpu,
+		.sync_single_for_device = loongson_dma_sync_single_for_device,
+		.sync_sg_for_cpu = swiotlb_sync_sg_for_cpu,
+		.sync_sg_for_device = loongson_dma_sync_sg_for_device,
+		.mapping_error = swiotlb_dma_mapping_error,
+		.dma_supported = swiotlb_dma_supported,
+		.set_dma_mask = loongson_dma_set_mask
+	},
+	.phys_to_dma = loongson_unity_phys_to_dma,
+	.dma_to_phys = loongson_unity_dma_to_phys

Why do you need these? I am not seeing it being used here by any external code?