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 --- 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/rockchip/rockchip_drm_gem.c | 26 ++++++++++++-------------- 1 file changed, 12 insertions(+), 14 deletions(-)
diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c index 0d18846..9df7d7d 100644 --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c @@ -36,8 +36,8 @@ static int rockchip_gem_iommu_map(struct rockchip_gem_object *rk_obj)
rk_obj->dma_addr = rk_obj->mm.start;
- ret = iommu_map_sg(private->domain, rk_obj->dma_addr, rk_obj->sgt->sgl, - rk_obj->sgt->nents, prot); + ret = iommu_map_sgtable(private->domain, rk_obj->dma_addr, rk_obj->sgt, + prot); if (ret < rk_obj->base.size) { DRM_ERROR("failed to map buffer: size=%zd request_size=%zd\n", ret, rk_obj->base.size); @@ -98,11 +98,10 @@ static int rockchip_gem_get_pages(struct rockchip_gem_object *rk_obj) * TODO: Replace this by drm_clflush_sg() once it can be implemented * without relying on symbols that are not exported. */ - for_each_sg(rk_obj->sgt->sgl, s, rk_obj->sgt->nents, i) + for_each_sg(rk_obj->sgt->sgl, s, rk_obj->sgt->orig_nents, i) sg_dma_address(s) = sg_phys(s);
- dma_sync_sg_for_device(drm->dev, rk_obj->sgt->sgl, rk_obj->sgt->nents, - DMA_TO_DEVICE); + dma_sync_sgtable_for_device(drm->dev, rk_obj->sgt, DMA_TO_DEVICE);
return 0;
@@ -350,8 +349,8 @@ void rockchip_gem_free_object(struct drm_gem_object *obj) if (private->domain) { rockchip_gem_iommu_unmap(rk_obj); } else { - dma_unmap_sg(drm->dev, rk_obj->sgt->sgl, - rk_obj->sgt->nents, DMA_BIDIRECTIONAL); + dma_unmap_sgtable(drm->dev, rk_obj->sgt, + DMA_BIDIRECTIONAL); } drm_prime_gem_destroy(obj, rk_obj->sgt); } else { @@ -493,15 +492,14 @@ static unsigned long rockchip_sg_get_contiguous_size(struct sg_table *sgt, struct sg_table *sg, struct rockchip_gem_object *rk_obj) { - int count = dma_map_sg(drm->dev, sg->sgl, sg->nents, - DMA_BIDIRECTIONAL); - if (!count) - return -EINVAL; + int err = dma_map_sgtable(drm->dev, sg, DMA_BIDIRECTIONAL); + if (err) + return err;
- if (rockchip_sg_get_contiguous_size(sg, count) < attach->dmabuf->size) { + if (rockchip_sg_get_contiguous_size(sg, sg->nents) < + attach->dmabuf->size) { DRM_ERROR("failed to map sg_table to contiguous linear address.\n"); - dma_unmap_sg(drm->dev, sg->sgl, sg->nents, - DMA_BIDIRECTIONAL); + dma_unmap_sgtable(drm->dev, sg, DMA_BIDIRECTIONAL); return -EINVAL; }