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    Subject[PATCH v7 15/36] drm: omapdrm: 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.

    Fix the code to refer to proper nents or orig_nents entries. This driver
    checks for a buffer contiguity in DMA address space, so it should test
    sg_table->nents entry.

    Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
    ---
    drivers/gpu/drm/omapdrm/omap_gem.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
    index ff0c4b0c3fd0..a7a9a0afe2b6 100644
    --- a/drivers/gpu/drm/omapdrm/omap_gem.c
    +++ b/drivers/gpu/drm/omapdrm/omap_gem.c
    @@ -48,7 +48,7 @@ struct omap_gem_object {
    * OMAP_BO_MEM_DMA_API flag set)
    *
    * - buffers imported from dmabuf (with the OMAP_BO_MEM_DMABUF flag set)
    - * if they are physically contiguous (when sgt->orig_nents == 1)
    + * if they are physically contiguous (when sgt->nents == 1)
    *
    * - buffers mapped through the TILER when dma_addr_cnt is not zero, in
    * which case the DMA address points to the TILER aperture
    @@ -1279,7 +1279,7 @@ struct drm_gem_object *omap_gem_new_dmabuf(struct drm_device *dev, size_t size,
    union omap_gem_size gsize;

    /* Without a DMM only physically contiguous buffers can be supported. */
    - if (sgt->orig_nents != 1 && !priv->has_dmm)
    + if (sgt->nents != 1 && !priv->has_dmm)
    return ERR_PTR(-EINVAL);

    gsize.bytes = PAGE_ALIGN(size);
    @@ -1293,7 +1293,7 @@ struct drm_gem_object *omap_gem_new_dmabuf(struct drm_device *dev, size_t size,

    omap_obj->sgt = sgt;

    - if (sgt->orig_nents == 1) {
    + if (sgt->nents == 1) {
    omap_obj->dma_addr = sg_dma_address(sgt->sgl);
    } else {
    /* Create pages list from sgt */
    --
    2.17.1
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