Commit efc42bc9 authored by Tomasz Stanislawski's avatar Tomasz Stanislawski Committed by Marek Szyprowski

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: default avatarTomasz Stanislawski <>
Signed-off-by: default avatarKyungmin Park <>
Acked-by: default avatarDaniel Vetter <>
Acked-by: default avatarLaurent Pinchart <>
Signed-off-by: default avatarMarek Szyprowski <>
CC: Andrew Morton <>
parent 28a33cbc
......@@ -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);
......@@ -318,6 +318,70 @@ int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
* 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)
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)
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;
* sg_miter_start - start mapping iteration over a sg list
* @miter: sg mapping iter to be started
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