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    Subject[PATCH v4 09/38] drm: etnaviv: 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>
    ---
    For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents
    vs. orig_nents misuse' thread:
    https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@samsung.com/T/
    ---
    drivers/gpu/drm/etnaviv/etnaviv_gem.c | 12 +++++-------
    drivers/gpu/drm/etnaviv/etnaviv_mmu.c | 13 +++----------
    2 files changed, 8 insertions(+), 17 deletions(-)

    diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
    index dc9ef30..cc50c7b 100644
    --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
    +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
    @@ -27,7 +27,7 @@ static void etnaviv_gem_scatter_map(struct etnaviv_gem_object *etnaviv_obj)
    * because display controller, GPU, etc. are not coherent.
    */
    if (etnaviv_obj->flags & ETNA_BO_CACHE_MASK)
    - dma_map_sg(dev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL);
    + dma_map_sgtable(dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
    }

    static void etnaviv_gem_scatterlist_unmap(struct etnaviv_gem_object *etnaviv_obj)
    @@ -51,7 +51,7 @@ static void etnaviv_gem_scatterlist_unmap(struct etnaviv_gem_object *etnaviv_obj
    * discard those writes.
    */
    if (etnaviv_obj->flags & ETNA_BO_CACHE_MASK)
    - dma_unmap_sg(dev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL);
    + dma_unmap_sgtable(dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
    }

    /* called with etnaviv_obj->lock held */
    @@ -404,9 +404,8 @@ int etnaviv_gem_cpu_prep(struct drm_gem_object *obj, u32 op,
    }

    if (etnaviv_obj->flags & ETNA_BO_CACHED) {
    - dma_sync_sg_for_cpu(dev->dev, etnaviv_obj->sgt->sgl,
    - etnaviv_obj->sgt->nents,
    - etnaviv_op_to_dma_dir(op));
    + dma_sync_sgtable_for_cpu(dev->dev, etnaviv_obj->sgt,
    + etnaviv_op_to_dma_dir(op));
    etnaviv_obj->last_cpu_prep_op = op;
    }

    @@ -421,8 +420,7 @@ int etnaviv_gem_cpu_fini(struct drm_gem_object *obj)
    if (etnaviv_obj->flags & ETNA_BO_CACHED) {
    /* fini without a prep is almost certainly a userspace error */
    WARN_ON(etnaviv_obj->last_cpu_prep_op == 0);
    - dma_sync_sg_for_device(dev->dev, etnaviv_obj->sgt->sgl,
    - etnaviv_obj->sgt->nents,
    + dma_sync_sgtable_for_device(dev->dev, etnaviv_obj->sgt,
    etnaviv_op_to_dma_dir(etnaviv_obj->last_cpu_prep_op));
    etnaviv_obj->last_cpu_prep_op = 0;
    }
    diff --git a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
    index 3607d34..13b1005 100644
    --- a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
    +++ b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
    @@ -79,7 +79,7 @@ static int etnaviv_iommu_map(struct etnaviv_iommu_context *context, u32 iova,
    if (!context || !sgt)
    return -EINVAL;

    - for_each_sg(sgt->sgl, sg, sgt->nents, i) {
    + for_each_sgtable_dma_sg(sgt, sg, i) {
    u32 pa = sg_dma_address(sg) - sg->offset;
    size_t bytes = sg_dma_len(sg) + sg->offset;

    @@ -95,14 +95,7 @@ static int etnaviv_iommu_map(struct etnaviv_iommu_context *context, u32 iova,
    return 0;

    fail:
    - da = iova;
    -
    - for_each_sg(sgt->sgl, sg, i, j) {
    - size_t bytes = sg_dma_len(sg) + sg->offset;
    -
    - etnaviv_context_unmap(context, da, bytes);
    - da += bytes;
    - }
    + etnaviv_context_unmap(context, iova, da - iova);
    return ret;
    }

    @@ -113,7 +106,7 @@ static void etnaviv_iommu_unmap(struct etnaviv_iommu_context *context, u32 iova,
    unsigned int da = iova;
    int i;

    - for_each_sg(sgt->sgl, sg, sgt->nents, i) {
    + for_each_sgtable_dma_sg(sgt, sg, i) {
    size_t bytes = sg_dma_len(sg) + sg->offset;

    etnaviv_context_unmap(context, da, bytes);
    --
    1.9.1
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