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authorTomasz Stanislawski <t.stanislaws@samsung.com>2012-06-18 09:25:01 +0200
committerMarek Szyprowski <m.szyprowski@samsung.com>2012-07-30 12:25:44 +0200
commitefc42bc98058a36d761b16a114823db1a902ed05 (patch)
tree3ba9403ec5b4a8619bde6a7fd1eaa3c14843ad3d /lib/scatterlist.c
parent28a33cbc24e4256c143dce96c7d93bf423229f92 (diff)
downloadlinux-stericsson-efc42bc98058a36d761b16a114823db1a902ed05.tar.gz
scatterlist: add sg_alloc_table_from_pages function
This patch adds a new constructor for an sg table. The table is constructed from an array of struct pages. All contiguous chunks of the pages are merged into a single sg nodes. A user may provide an offset and a size of a buffer if the buffer is not page-aligned. The function is dedicated for DMABUF exporters which often perform conversion from an page array to a scatterlist. Moreover the scatterlist should be squashed in order to save memory and to speed-up the process of DMA mapping using dma_map_sg. The code is based on the patch 'v4l: vb2-dma-contig: add support for scatterlist in userptr mode' and hints from Laurent Pinchart. Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> CC: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'lib/scatterlist.c')
-rw-r--r--lib/scatterlist.c64
1 files changed, 64 insertions, 0 deletions
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 6096e89bee55..e719adf695bf 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -319,6 +319,70 @@ int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
EXPORT_SYMBOL(sg_alloc_table);
/**
+ * sg_alloc_table_from_pages - Allocate and initialize an sg table from
+ * an array of pages
+ * @sgt: The sg table header to use
+ * @pages: Pointer to an array of page pointers
+ * @n_pages: Number of pages in the pages array
+ * @offset: Offset from start of the first page to the start of a buffer
+ * @size: Number of valid bytes in the buffer (after offset)
+ * @gfp_mask: GFP allocation mask
+ *
+ * Description:
+ * Allocate and initialize an sg table from a list of pages. Contiguous
+ * ranges of the pages are squashed into a single scatterlist node. A user
+ * may provide an offset at a start and a size of valid data in a buffer
+ * specified by the page array. The returned sg table is released by
+ * sg_free_table.
+ *
+ * Returns:
+ * 0 on success, negative error on failure
+ */
+int sg_alloc_table_from_pages(struct sg_table *sgt,
+ struct page **pages, unsigned int n_pages,
+ unsigned long offset, unsigned long size,
+ gfp_t gfp_mask)
+{
+ unsigned int chunks;
+ unsigned int i;
+ unsigned int cur_page;
+ int ret;
+ struct scatterlist *s;
+
+ /* compute number of contiguous chunks */
+ chunks = 1;
+ for (i = 1; i < n_pages; ++i)
+ if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1)
+ ++chunks;
+
+ ret = sg_alloc_table(sgt, chunks, gfp_mask);
+ if (unlikely(ret))
+ return ret;
+
+ /* merging chunks and putting them into the scatterlist */
+ cur_page = 0;
+ for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
+ unsigned long chunk_size;
+ unsigned int j;
+
+ /* look for the end of the current chunk */
+ for (j = cur_page + 1; j < n_pages; ++j)
+ if (page_to_pfn(pages[j]) !=
+ page_to_pfn(pages[j - 1]) + 1)
+ break;
+
+ chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
+ sg_set_page(s, pages[cur_page], min(size, chunk_size), offset);
+ size -= chunk_size;
+ offset = 0;
+ cur_page = j;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL(sg_alloc_table_from_pages);
+
+/**
* sg_miter_start - start mapping iteration over a sg list
* @miter: sg mapping iter to be started
* @sgl: sg list to iterate over