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);