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SubjectRe: [PATCH v3 10/25] drm: panfrost: fix common struct sg_table related issues
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On 05/05/2020 09:45, Marek Szyprowski wrote:
> The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the
> numer of the created entries in the DMA address space. However the
> subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be
> called with the original number of the entries passed to dma_map_sg. The
> sg_table->nents in turn holds the result of the dma_map_sg call as stated
> in include/linux/scatterlist.h. A common mistake was to ignore a result
> of the dma_map_sg function and don't use the sg_table->orig_nents at all.
>
> To avoid such issues, lets use common dma-mapping wrappers operating
> directly on the struct sg_table objects and adjust references to the
> nents and orig_nents respectively.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

The change looks good to me:

Reviewed-by: Steven Price <steven.price@arm.com>

Although I would have appreciated the commit message being modified to
match the specifics of Panfrost - the return of dma_mpa_sg() wasn't
being ignored, but the use of orig_nents/nents was indeed wrong.

Steve

> ---
> For more information, see '[PATCH v3 00/25] DRM: fix struct sg_table nents
> vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/5/187
> ---
> drivers/gpu/drm/panfrost/panfrost_gem.c | 4 ++--
> drivers/gpu/drm/panfrost/panfrost_mmu.c | 5 ++---
> 2 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index 17b654e..95d7e80 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);
> 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 ed28aeb..9926111 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -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);
> + if (ret)
> goto err_map;
> - }
>
> mmu_map_sg(pfdev, bomapping->mmu, addr,
> IOMMU_WRITE | IOMMU_READ | IOMMU_NOEXEC, sgt);
>

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