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    Subject[PATCH v6 31/36] misc: fastrpc: fix common struct sg_table related issues
    Date
    The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
    returns the number of the created entries in the DMA address space.
    However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
    dma_unmap_sg must be called with the original number of the entries
    passed to the dma_map_sg().

    struct sg_table is a common structure used for describing a non-contiguous
    memory buffer, used commonly in the DRM and graphics subsystems. It
    consists of a scatterlist with memory pages and DMA addresses (sgl entry),
    as well as the number of scatterlist entries: CPU pages (orig_nents entry)
    and DMA mapped pages (nents entry).

    It turned out that it was a common mistake to misuse nents and orig_nents
    entries, calling DMA-mapping functions with a wrong number of entries or
    ignoring the number of mapped entries returned by the dma_map_sg()
    function.

    To avoid such issues, lets use a common dma-mapping wrappers operating
    directly on the struct sg_table objects and use scatterlist page
    iterators where possible. This, almost always, hides references to the
    nents and orig_nents entries, making the code robust, easier to follow
    and copy/paste safe.

    Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
    ---
    drivers/misc/fastrpc.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
    index 7939c55daceb..9d6867749316 100644
    --- a/drivers/misc/fastrpc.c
    +++ b/drivers/misc/fastrpc.c
    @@ -518,7 +518,7 @@ fastrpc_map_dma_buf(struct dma_buf_attachment *attachment,

    table = &a->sgt;

    - if (!dma_map_sg(attachment->dev, table->sgl, table->nents, dir))
    + if (!dma_map_sgtable(attachment->dev, table, dir, 0))
    return ERR_PTR(-ENOMEM);

    return table;
    @@ -528,7 +528,7 @@ static void fastrpc_unmap_dma_buf(struct dma_buf_attachment *attach,
    struct sg_table *table,
    enum dma_data_direction dir)
    {
    - dma_unmap_sg(attach->dev, table->sgl, table->nents, dir);
    + dma_unmap_sgtable(attach->dev, table, dir, 0);
    }

    static void fastrpc_release(struct dma_buf *dmabuf)
    --
    2.17.1
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