Hi Tomasz,

Thank you for the patch.

On Tuesday 08 May 2012 11:50:33 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 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 at samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>

Acked-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> ---
>  include/linux/scatterlist.h |    4 +++
>  lib/scatterlist.c           |   64
> +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 68
> insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index ac9586d..7b600da 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 6096e89..85868a1 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. 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, 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;
> +
> +             /* looking 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

-- 
Regards,

Laurent Pinchart

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