linux-kernel - [PATCH 2/6] dma-mapping: add a dma_mmap

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Date:   Thu, 28 Jan 2021 15:58:33 +0100
From:   Christoph Hellwig <hch@....de>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Ricardo Ribalda <ribalda@...omium.org>,
        Sergey Senozhatsky <senozhatsky@...gle.com>,
        iommu@...ts.linux-foundation.org
Cc:     Robin Murphy <robin.murphy@....com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: [PATCH 2/6] 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@....de>
---
 Documentation/core-api/dma-api.rst | 10 ++++++++++
 include/linux/dma-mapping.h        |  2 ++
 kernel/dma/mapping.c               | 13 +++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
index e6d23f117308df..157a474ae54416 100644
--- a/Documentation/core-api/dma-api.rst
+++ b/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 *
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index fbfa3f5abd9498..4977a748cb9483 100644
--- a/include/linux/dma-mapping.h
+++ b/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)
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 68992e35c8c3a7..c1e515496c067b 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -515,6 +515,19 @@ 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);
-- 
2.29.2