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

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 <t.stanislaws@samsung.com>
Signed-off-by: default avatarKyungmin Park <kyungmin.park@samsung.com>
Acked-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: default avatarLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
CC: Andrew Morton <akpm@linux-foundation.org>
parent 28a33cbc

include/linux/scatterlist.h

+4 −0
Original line number Diff line number Diff line
@@ -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);

lib/scatterlist.c

+64 −0
Original line number Diff line number Diff line
@@ -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