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    Subject[PATCH v7 13/36] drm: msm: 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>
    ---
    drivers/gpu/drm/msm/msm_gem.c | 13 +++++--------
    drivers/gpu/drm/msm/msm_gpummu.c | 14 ++++++--------
    drivers/gpu/drm/msm/msm_iommu.c | 2 +-
    3 files changed, 12 insertions(+), 17 deletions(-)

    diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
    index 38b0c0e1f83e..e0d5fd36ea8f 100644
    --- a/drivers/gpu/drm/msm/msm_gem.c
    +++ b/drivers/gpu/drm/msm/msm_gem.c
    @@ -53,11 +53,10 @@ static void sync_for_device(struct msm_gem_object *msm_obj)
    struct device *dev = msm_obj->base.dev->dev;

    if (get_dma_ops(dev) && IS_ENABLED(CONFIG_ARM64)) {
    - dma_sync_sg_for_device(dev, msm_obj->sgt->sgl,
    - msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
    + dma_sync_sgtable_for_device(dev, msm_obj->sgt,
    + DMA_BIDIRECTIONAL);
    } else {
    - dma_map_sg(dev, msm_obj->sgt->sgl,
    - msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
    + dma_map_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0);
    }
    }

    @@ -66,11 +65,9 @@ static void sync_for_cpu(struct msm_gem_object *msm_obj)
    struct device *dev = msm_obj->base.dev->dev;

    if (get_dma_ops(dev) && IS_ENABLED(CONFIG_ARM64)) {
    - dma_sync_sg_for_cpu(dev, msm_obj->sgt->sgl,
    - msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
    + dma_sync_sgtable_for_cpu(dev, msm_obj->sgt, DMA_BIDIRECTIONAL);
    } else {
    - dma_unmap_sg(dev, msm_obj->sgt->sgl,
    - msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
    + dma_unmap_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0);
    }
    }

    diff --git a/drivers/gpu/drm/msm/msm_gpummu.c b/drivers/gpu/drm/msm/msm_gpummu.c
    index 310a31b05faa..319f06c28235 100644
    --- a/drivers/gpu/drm/msm/msm_gpummu.c
    +++ b/drivers/gpu/drm/msm/msm_gpummu.c
    @@ -30,21 +30,19 @@ static int msm_gpummu_map(struct msm_mmu *mmu, uint64_t iova,
    {
    struct msm_gpummu *gpummu = to_msm_gpummu(mmu);
    unsigned idx = (iova - GPUMMU_VA_START) / GPUMMU_PAGE_SIZE;
    - struct scatterlist *sg;
    + struct sg_dma_page_iter dma_iter;
    unsigned prot_bits = 0;
    - unsigned i, j;

    if (prot & IOMMU_WRITE)
    prot_bits |= 1;
    if (prot & IOMMU_READ)
    prot_bits |= 2;

    - for_each_sg(sgt->sgl, sg, sgt->nents, i) {
    - dma_addr_t addr = sg->dma_address;
    - for (j = 0; j < sg->length / GPUMMU_PAGE_SIZE; j++, idx++) {
    - gpummu->table[idx] = addr | prot_bits;
    - addr += GPUMMU_PAGE_SIZE;
    - }
    + for_each_sgtable_dma_page(sgt, &dma_iter, 0) {
    + dma_addr_t addr = sg_page_iter_dma_address(&dma_iter);
    +
    + BUILD_BUG_ON(GPUMMU_PAGE_SIZE != PAGE_SIZE);
    + gpummu->table[idx++] = addr | prot_bits;
    }

    /* we can improve by deferring flush for multiple map() */
    diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
    index 3a381a9674c9..6c31e65834c6 100644
    --- a/drivers/gpu/drm/msm/msm_iommu.c
    +++ b/drivers/gpu/drm/msm/msm_iommu.c
    @@ -36,7 +36,7 @@ static int msm_iommu_map(struct msm_mmu *mmu, uint64_t iova,
    struct msm_iommu *iommu = to_msm_iommu(mmu);
    size_t ret;

    - ret = iommu_map_sg(iommu->domain, iova, sgt->sgl, sgt->nents, prot);
    + ret = iommu_map_sgtable(iommu->domain, iova, sgt, prot);
    WARN_ON(!ret);

    return (ret == len) ? 0 : -EINVAL;
    --
    2.17.1
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