Hi Tomasz,
Thanks for the patch.
On Wednesday 18 April 2012 11:44:59 Tomasz Stanislawski wrote:
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 performs conversion from an page array to a scatterlist. Moreover the scatterlist should be squashed in order to save memory and to speed-up 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.
The patch looks good to me. Just a small comment, what do you think about naming the function sg_alloc_table_from_pages instead of sg_table_alloc_by_pages ?
Signed-off-by: Tomasz Stanislawski t.stanislaws@samsung.com Signed-off-by: Kyungmin Park kyungmin.park@samsung.com
include/linux/scatterlist.h | 4 +++ lib/scatterlist.c | 63 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 67 insertions(+), 0 deletions(-)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index ac9586d..8d9e6fe 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_by_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 6096e89..30b9def 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -319,6 +319,69 @@ int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask) EXPORT_SYMBOL(sg_alloc_table);
/**
- sg_alloc_table_by_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. Continuous
- 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
Maybe you should mention what it returns in case of an error as well.
- **/
+int sg_alloc_table_by_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 (pages[i] != 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;/* looking for the end of the current chunk */for (j = cur_page + 1; j < n_pages; ++j)if (pages[j] != 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_by_pages);
+/**
- sg_miter_start - start mapping iteration over a sg list
- @miter: sg mapping iter to be started
- @sgl: sg list to iterate over