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    Subject[PATCH v7 28/36] dmabuf: 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>
    Acked-by: Gerd Hoffmann <kraxel@redhat.com>
    ---
    drivers/dma-buf/heaps/heap-helpers.c | 13 ++++++-------
    drivers/dma-buf/udmabuf.c | 7 +++----
    2 files changed, 9 insertions(+), 11 deletions(-)

    diff --git a/drivers/dma-buf/heaps/heap-helpers.c b/drivers/dma-buf/heaps/heap-helpers.c
    index 9f964ca3f59c..d0696cf937af 100644
    --- a/drivers/dma-buf/heaps/heap-helpers.c
    +++ b/drivers/dma-buf/heaps/heap-helpers.c
    @@ -140,13 +140,12 @@ struct sg_table *dma_heap_map_dma_buf(struct dma_buf_attachment *attachment,
    enum dma_data_direction direction)
    {
    struct dma_heaps_attachment *a = attachment->priv;
    - struct sg_table *table;
    -
    - table = &a->table;
    + struct sg_table *table = &a->table;
    + int ret;

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

    @@ -154,7 +153,7 @@ static void dma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
    struct sg_table *table,
    enum dma_data_direction direction)
    {
    - dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
    + dma_unmap_sgtable(attachment->dev, table, direction, 0);
    }

    static vm_fault_t dma_heap_vm_fault(struct vm_fault *vmf)
    diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
    index acb26c627d27..89e293bd9252 100644
    --- a/drivers/dma-buf/udmabuf.c
    +++ b/drivers/dma-buf/udmabuf.c
    @@ -63,10 +63,9 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
    GFP_KERNEL);
    if (ret < 0)
    goto err;
    - if (!dma_map_sg(dev, sg->sgl, sg->nents, direction)) {
    - ret = -EINVAL;
    + ret = dma_map_sgtable(dev, sg, direction, 0);
    + if (ret < 0)
    goto err;
    - }
    return sg;

    err:
    @@ -78,7 +77,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
    static void put_sg_table(struct device *dev, struct sg_table *sg,
    enum dma_data_direction direction)
    {
    - dma_unmap_sg(dev, sg->sgl, sg->nents, direction);
    + dma_unmap_sgtable(dev, sg, direction, 0);
    sg_free_table(sg);
    kfree(sg);
    }
    --
    2.17.1
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