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    Subject[PATCH v10 17/30] drm: tegra: fix common struct sg_table related issues
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    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>
    Reviewed-by: Robin Murphy <robin.murphy@arm.com>
    ---
    drivers/gpu/drm/tegra/gem.c | 27 ++++++++++-----------------
    drivers/gpu/drm/tegra/plane.c | 15 +++++----------
    2 files changed, 15 insertions(+), 27 deletions(-)

    diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
    index 723df142a981..01d94befab11 100644
    --- a/drivers/gpu/drm/tegra/gem.c
    +++ b/drivers/gpu/drm/tegra/gem.c
    @@ -98,8 +98,8 @@ static struct sg_table *tegra_bo_pin(struct device *dev, struct host1x_bo *bo,
    * the SG table needs to be copied to avoid overwriting any
    * other potential users of the original SG table.
    */
    - err = sg_alloc_table_from_sg(sgt, obj->sgt->sgl, obj->sgt->nents,
    - GFP_KERNEL);
    + err = sg_alloc_table_from_sg(sgt, obj->sgt->sgl,
    + obj->sgt->orig_nents, GFP_KERNEL);
    if (err < 0)
    goto free;
    } else {
    @@ -196,8 +196,7 @@ static int tegra_bo_iommu_map(struct tegra_drm *tegra, struct tegra_bo *bo)

    bo->iova = bo->mm->start;

    - bo->size = iommu_map_sg(tegra->domain, bo->iova, bo->sgt->sgl,
    - bo->sgt->nents, prot);
    + bo->size = iommu_map_sgtable(tegra->domain, bo->iova, bo->sgt, prot);
    if (!bo->size) {
    dev_err(tegra->drm->dev, "failed to map buffer\n");
    err = -ENOMEM;
    @@ -264,8 +263,7 @@ static struct tegra_bo *tegra_bo_alloc_object(struct drm_device *drm,
    static void tegra_bo_free(struct drm_device *drm, struct tegra_bo *bo)
    {
    if (bo->pages) {
    - dma_unmap_sg(drm->dev, bo->sgt->sgl, bo->sgt->nents,
    - DMA_FROM_DEVICE);
    + dma_unmap_sgtable(drm->dev, bo->sgt, DMA_FROM_DEVICE, 0);
    drm_gem_put_pages(&bo->gem, bo->pages, true, true);
    sg_free_table(bo->sgt);
    kfree(bo->sgt);
    @@ -290,12 +288,9 @@ static int tegra_bo_get_pages(struct drm_device *drm, struct tegra_bo *bo)
    goto put_pages;
    }

    - err = dma_map_sg(drm->dev, bo->sgt->sgl, bo->sgt->nents,
    - DMA_FROM_DEVICE);
    - if (err == 0) {
    - err = -EFAULT;
    + err = dma_map_sgtable(drm->dev, bo->sgt, DMA_FROM_DEVICE, 0);
    + if (err)
    goto free_sgt;
    - }

    return 0;

    @@ -571,7 +566,7 @@ tegra_gem_prime_map_dma_buf(struct dma_buf_attachment *attach,
    goto free;
    }

    - if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0)
    + if (dma_map_sgtable(attach->dev, sgt, dir, 0))
    goto free;

    return sgt;
    @@ -590,7 +585,7 @@ static void tegra_gem_prime_unmap_dma_buf(struct dma_buf_attachment *attach,
    struct tegra_bo *bo = to_tegra_bo(gem);

    if (bo->pages)
    - dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir);
    + dma_unmap_sgtable(attach->dev, sgt, dir, 0);

    sg_free_table(sgt);
    kfree(sgt);
    @@ -609,8 +604,7 @@ static int tegra_gem_prime_begin_cpu_access(struct dma_buf *buf,
    struct drm_device *drm = gem->dev;

    if (bo->pages)
    - dma_sync_sg_for_cpu(drm->dev, bo->sgt->sgl, bo->sgt->nents,
    - DMA_FROM_DEVICE);
    + dma_sync_sgtable_for_cpu(drm->dev, bo->sgt, DMA_FROM_DEVICE);

    return 0;
    }
    @@ -623,8 +617,7 @@ static int tegra_gem_prime_end_cpu_access(struct dma_buf *buf,
    struct drm_device *drm = gem->dev;

    if (bo->pages)
    - dma_sync_sg_for_device(drm->dev, bo->sgt->sgl, bo->sgt->nents,
    - DMA_TO_DEVICE);
    + dma_sync_sgtable_for_device(drm->dev, bo->sgt, DMA_TO_DEVICE);

    return 0;
    }
    diff --git a/drivers/gpu/drm/tegra/plane.c b/drivers/gpu/drm/tegra/plane.c
    index 4cd0461cc508..539d14935728 100644
    --- a/drivers/gpu/drm/tegra/plane.c
    +++ b/drivers/gpu/drm/tegra/plane.c
    @@ -131,12 +131,9 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
    }

    if (sgt) {
    - err = dma_map_sg(dc->dev, sgt->sgl, sgt->nents,
    - DMA_TO_DEVICE);
    - if (err == 0) {
    - err = -ENOMEM;
    + err = dma_map_sgtable(dc->dev, sgt, DMA_TO_DEVICE, 0);
    + if (err)
    goto unpin;
    - }

    /*
    * The display controller needs contiguous memory, so
    @@ -144,7 +141,7 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
    * map its SG table to a single contiguous chunk of
    * I/O virtual memory.
    */
    - if (err > 1) {
    + if (sgt->nents > 1) {
    err = -EINVAL;
    goto unpin;
    }
    @@ -166,8 +163,7 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
    struct sg_table *sgt = state->sgt[i];

    if (sgt)
    - dma_unmap_sg(dc->dev, sgt->sgl, sgt->nents,
    - DMA_TO_DEVICE);
    + dma_unmap_sgtable(dc->dev, sgt, DMA_TO_DEVICE, 0);

    host1x_bo_unpin(dc->dev, &bo->base, sgt);
    state->iova[i] = DMA_MAPPING_ERROR;
    @@ -186,8 +182,7 @@ static void tegra_dc_unpin(struct tegra_dc *dc, struct tegra_plane_state *state)
    struct sg_table *sgt = state->sgt[i];

    if (sgt)
    - dma_unmap_sg(dc->dev, sgt->sgl, sgt->nents,
    - DMA_TO_DEVICE);
    + dma_unmap_sgtable(dc->dev, sgt, DMA_TO_DEVICE, 0);

    host1x_bo_unpin(dc->dev, &bo->base, sgt);
    state->iova[i] = DMA_MAPPING_ERROR;
    --
    2.17.1
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