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    Subject[PATCH v3 04/25] drm: armada: fix common struct sg_table related issues
    Date
    The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the
    numer of the created entries in the DMA address space. However the
    subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be
    called with the original number of the entries passed to dma_map_sg. The
    sg_table->nents in turn holds the result of the dma_map_sg call as stated
    in include/linux/scatterlist.h. A common mistake was to ignore a result
    of the dma_map_sg function and don't use the sg_table->orig_nents at all.

    To avoid such issues, lets use common dma-mapping wrappers operating
    directly on the struct sg_table objects and adjust references to the
    nents and orig_nents respectively.

    Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
    ---
    For more information, see '[PATCH v3 00/25] DRM: fix struct sg_table nents
    vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/5/187
    ---
    drivers/gpu/drm/armada/armada_gem.c | 10 +++++-----
    1 file changed, 5 insertions(+), 5 deletions(-)

    diff --git a/drivers/gpu/drm/armada/armada_gem.c b/drivers/gpu/drm/armada/armada_gem.c
    index 976685f..5b4f48c 100644
    --- a/drivers/gpu/drm/armada/armada_gem.c
    +++ b/drivers/gpu/drm/armada/armada_gem.c
    @@ -407,8 +407,8 @@ int armada_gem_pwrite_ioctl(struct drm_device *dev, void *data,
    sg_set_page(sg, page, PAGE_SIZE, 0);
    }

    - if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0) {
    - num = sgt->nents;
    + if (dma_map_sgtable(attach->dev, sgt, dir)) {
    + num = count;
    goto release;
    }
    } else if (dobj->page) {
    @@ -418,7 +418,7 @@ int armada_gem_pwrite_ioctl(struct drm_device *dev, void *data,

    sg_set_page(sgt->sgl, dobj->page, dobj->obj.size, 0);

    - if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0)
    + if (dma_map_sgtable(attach->dev, sgt, dir))
    goto free_table;
    } else if (dobj->linear) {
    /* Single contiguous physical region - no struct page */
    @@ -449,11 +449,11 @@ static void armada_gem_prime_unmap_dma_buf(struct dma_buf_attachment *attach,
    int i;

    if (!dobj->linear)
    - dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir);
    + dma_unmap_sgtable(attach->dev, sgt, dir);

    if (dobj->obj.filp) {
    struct scatterlist *sg;
    - for_each_sg(sgt->sgl, sg, sgt->nents, i)
    + for_each_sg(sgt->sgl, sg, sgt->orig_nents, i)
    put_page(sg_page(sg));
    }

    --
    1.9.1
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