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    Subject[PATCH v6 25/36] drm: host1x: 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/host1x/job.c | 22 ++++++++--------------
    1 file changed, 8 insertions(+), 14 deletions(-)

    diff --git a/drivers/gpu/host1x/job.c b/drivers/gpu/host1x/job.c
    index a10643aa89aa..4832b57f10c4 100644
    --- a/drivers/gpu/host1x/job.c
    +++ b/drivers/gpu/host1x/job.c
    @@ -166,11 +166,9 @@ static unsigned int pin_job(struct host1x *host, struct host1x_job *job)
    goto unpin;
    }

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

    job->unpins[job->num_unpins].dev = dev;
    job->unpins[job->num_unpins].dir = dir;
    @@ -217,7 +215,7 @@ static unsigned int pin_job(struct host1x *host, struct host1x_job *job)
    }

    if (!IS_ENABLED(CONFIG_TEGRA_HOST1X_FIREWALL) && host->domain) {
    - for_each_sg(sgt->sgl, sg, sgt->nents, j)
    + for_each_sgtable_sg(sgt, sg, j)
    gather_size += sg->length;
    gather_size = iova_align(&host->iova, gather_size);

    @@ -229,9 +227,9 @@ static unsigned int pin_job(struct host1x *host, struct host1x_job *job)
    goto unpin;
    }

    - err = iommu_map_sg(host->domain,
    + err = iommu_map_sgtable(host->domain,
    iova_dma_addr(&host->iova, alloc),
    - sgt->sgl, sgt->nents, IOMMU_READ);
    + sgt, IOMMU_READ);
    if (err == 0) {
    __free_iova(&host->iova, alloc);
    err = -EINVAL;
    @@ -241,12 +239,9 @@ static unsigned int pin_job(struct host1x *host, struct host1x_job *job)
    job->unpins[job->num_unpins].size = gather_size;
    phys_addr = iova_dma_addr(&host->iova, alloc);
    } else if (sgt) {
    - err = dma_map_sg(host->dev, sgt->sgl, sgt->nents,
    - DMA_TO_DEVICE);
    - if (!err) {
    - err = -ENOMEM;
    + err = dma_map_sgtable(host->dev, sgt, DMA_TO_DEVICE, 0);
    + if (err)
    goto unpin;
    - }

    job->unpins[job->num_unpins].dir = DMA_TO_DEVICE;
    job->unpins[job->num_unpins].dev = host->dev;
    @@ -647,8 +642,7 @@ void host1x_job_unpin(struct host1x_job *job)
    }

    if (unpin->dev && sgt)
    - dma_unmap_sg(unpin->dev, sgt->sgl, sgt->nents,
    - unpin->dir);
    + dma_unmap_sgtable(unpin->dev, sgt, unpin->dir, 0);

    host1x_bo_unpin(dev, unpin->bo, sgt);
    host1x_bo_put(unpin->bo);
    --
    2.17.1
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