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    Subject[PATCH v7 27/36] drm: rcar-du: 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.

    dma_map_sgtable() function returns zero or an error code, so adjust the
    return value check for the vsp1_du_map_sg() function.

    Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
    Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
    ---
    drivers/gpu/drm/rcar-du/rcar_du_vsp.c | 3 +--
    drivers/media/platform/vsp1/vsp1_drm.c | 8 ++++----
    2 files changed, 5 insertions(+), 6 deletions(-)

    diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
    index f1a81c9b184d..a27bff999649 100644
    --- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
    +++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
    @@ -197,9 +197,8 @@ int rcar_du_vsp_map_fb(struct rcar_du_vsp *vsp, struct drm_framebuffer *fb,
    goto fail;

    ret = vsp1_du_map_sg(vsp->vsp, sgt);
    - if (!ret) {
    + if (ret) {
    sg_free_table(sgt);
    - ret = -ENOMEM;
    goto fail;
    }
    }
    diff --git a/drivers/media/platform/vsp1/vsp1_drm.c b/drivers/media/platform/vsp1/vsp1_drm.c
    index a4a45d68a6ef..86d5e3f4b1ff 100644
    --- a/drivers/media/platform/vsp1/vsp1_drm.c
    +++ b/drivers/media/platform/vsp1/vsp1_drm.c
    @@ -912,8 +912,8 @@ int vsp1_du_map_sg(struct device *dev, struct sg_table *sgt)
    * skip cache sync. This will need to be revisited when support for
    * non-coherent buffers will be added to the DU driver.
    */
    - return dma_map_sg_attrs(vsp1->bus_master, sgt->sgl, sgt->nents,
    - DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
    + return dma_map_sgtable(vsp1->bus_master, sgt, DMA_TO_DEVICE,
    + DMA_ATTR_SKIP_CPU_SYNC);
    }
    EXPORT_SYMBOL_GPL(vsp1_du_map_sg);

    @@ -921,8 +921,8 @@ void vsp1_du_unmap_sg(struct device *dev, struct sg_table *sgt)
    {
    struct vsp1_device *vsp1 = dev_get_drvdata(dev);

    - dma_unmap_sg_attrs(vsp1->bus_master, sgt->sgl, sgt->nents,
    - DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
    + dma_unmap_sgtable(vsp1->bus_master, sgt, DMA_TO_DEVICE,
    + DMA_ATTR_SKIP_CPU_SYNC);
    }
    EXPORT_SYMBOL_GPL(vsp1_du_unmap_sg);

    --
    2.17.1
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