dma: Introduce dma_max_mapping_size()

The function returns the maximum size that can be mapped
using DMA-API functions. The patch also adds the
implementation for direct DMA and a new dma_map_ops pointer
so that other implementations can expose their limit.

Cc: stable@vger.kernel.org
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

kernel/dma/direct.c

@@ -380,3 +380,14 @@ int dma_direct_supported(struct device *dev, u64 mask)
 	 */
 	return mask >= __phys_to_dma(dev, min_mask);
 }
+
+size_t dma_direct_max_mapping_size(struct device *dev)
+{
+	size_t size = SIZE_MAX;
+
+	/* If SWIOTLB is active, use its maximum mapping size */
+	if (is_swiotlb_active())
+		size = swiotlb_max_mapping_size(dev);
+
+	return size;
+}

kernel/dma/mapping.c

@@ -357,3 +357,17 @@ void dma_cache_sync(struct device *dev, void *vaddr, size_t size,
 		ops->cache_sync(dev, vaddr, size, dir);
 }
 EXPORT_SYMBOL(dma_cache_sync);
+
+size_t dma_max_mapping_size(struct device *dev)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+	size_t size = SIZE_MAX;
+
+	if (dma_is_direct(ops))
+		size = dma_direct_max_mapping_size(dev);
+	else if (ops && ops->max_mapping_size)
+		size = ops->max_mapping_size(dev);
+
+	return size;
+}
+EXPORT_SYMBOL_GPL(dma_max_mapping_size);