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    Subject[PATCH v7 16/36] drm: panfrost: 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>
    Reviewed-by: Steven Price <steven.price@arm.com>
    Reviewed-by: Rob Herring <robh@kernel.org>
    ---
    drivers/gpu/drm/panfrost/panfrost_gem.c | 4 ++--
    drivers/gpu/drm/panfrost/panfrost_mmu.c | 7 +++----
    2 files changed, 5 insertions(+), 6 deletions(-)

    diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
    index ac5d0aa80276..ba8450ea04d0 100644
    --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
    +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
    @@ -41,8 +41,8 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj)

    for (i = 0; i < n_sgt; i++) {
    if (bo->sgts[i].sgl) {
    - dma_unmap_sg(pfdev->dev, bo->sgts[i].sgl,
    - bo->sgts[i].nents, DMA_BIDIRECTIONAL);
    + dma_unmap_sgtable(pfdev->dev, &bo->sgts[i],
    + DMA_BIDIRECTIONAL, 0);
    sg_free_table(&bo->sgts[i]);
    }
    }
    diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
    index 0a339c6fbfaa..fd294f6a7d3b 100644
    --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
    +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
    @@ -253,7 +253,7 @@ static int mmu_map_sg(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,
    struct io_pgtable_ops *ops = mmu->pgtbl_ops;
    u64 start_iova = iova;

    - for_each_sg(sgt->sgl, sgl, sgt->nents, count) {
    + for_each_sgtable_dma_sg(sgt, sgl, count) {
    unsigned long paddr = sg_dma_address(sgl);
    size_t len = sg_dma_len(sgl);

    @@ -517,10 +517,9 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
    if (ret)
    goto err_pages;

    - if (!dma_map_sg(pfdev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL)) {
    - ret = -EINVAL;
    + ret = dma_map_sgtable(pfdev->dev, sgt, DMA_BIDIRECTIONAL, 0);
    + if (ret)
    goto err_map;
    - }

    mmu_map_sg(pfdev, bomapping->mmu, addr,
    IOMMU_WRITE | IOMMU_READ | IOMMU_NOEXEC, sgt);
    --
    2.17.1
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