From efc42bc98058a36d761b16a114823db1a902ed05 Mon Sep 17 00:00:00 2001 From: Tomasz Stanislawski Date: Mon, 18 Jun 2012 09:25:01 +0200 Subject: [PATCH] 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 Signed-off-by: Kyungmin Park Acked-by: Daniel Vetter Acked-by: Laurent Pinchart Signed-off-by: Marek Szyprowski CC: Andrew Morton --- include/linux/scatterlist.h | 4 +++ lib/scatterlist.c | 64 +++++++++++++++++++++++++++++++++++++ 2 files changed, 68 insertions(+) diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index ac9586dadfa5..7b600da9a635 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -214,6 +214,10 @@ void sg_free_table(struct sg_table *); int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int, gfp_t, sg_alloc_fn *); int sg_alloc_table(struct sg_table *, unsigned int, gfp_t); +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); size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents, void *buf, size_t buflen); diff --git a/lib/scatterlist.c b/lib/scatterlist.c index 6096e89bee55..e719adf695bf 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -318,6 +318,70 @@ 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