dma-mapping: add a dma_mmap_pages helper

Add a helper to map memory allocated using dma_alloc_pages into
a user address space, similar to the dma_alloc_attrs function for
coherent allocations.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Tested-by: Ricardo Ribalda <ribalda@chromium.org>

Documentation/core-api/dma-api.rst

@@ -563,6 +563,16 @@ Free a region of memory previously allocated using dma_alloc_pages().
 dev, size, dma_handle and dir must all be the same as those passed into
 dma_alloc_pages().  page must be the pointer returned by dma_alloc_pages().
 
+::
+
+	int
+	dma_mmap_pages(struct device *dev, struct vm_area_struct *vma,
+		       size_t size, struct page *page)
+
+Map an allocation returned from dma_alloc_pages() into a user address space.
+dev and size must be the same as those passed into dma_alloc_pages().
+page must be the pointer returned by dma_alloc_pages().
+
 ::
 
 	void *

include/linux/dma-mapping.h

@@ -263,6 +263,8 @@ struct page *dma_alloc_pages(struct device *dev, size_t size,
 		dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp);
 void dma_free_pages(struct device *dev, size_t size, struct page *page,
 		dma_addr_t dma_handle, enum dma_data_direction dir);
+int dma_mmap_pages(struct device *dev, struct vm_area_struct *vma,
+		size_t size, struct page *page);
 
 static inline void *dma_alloc_noncoherent(struct device *dev, size_t size,
 		dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp)

kernel/dma/mapping.c

@@ -517,6 +517,19 @@ void dma_free_pages(struct device *dev, size_t size, struct page *page,
 }
 EXPORT_SYMBOL_GPL(dma_free_pages);
 
+int dma_mmap_pages(struct device *dev, struct vm_area_struct *vma,
+		size_t size, struct page *page)
+{
+	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+
+	if (vma->vm_pgoff >= count || vma_pages(vma) > count - vma->vm_pgoff)
+		return -ENXIO;
+	return remap_pfn_range(vma, vma->vm_start,
+			       page_to_pfn(page) + vma->vm_pgoff,
+			       vma_pages(vma) << PAGE_SHIFT, vma->vm_page_prot);
+}
+EXPORT_SYMBOL_GPL(dma_mmap_pages);
+
 int dma_supported(struct device *dev, u64 mask)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);