| Message ID | 20200513133245.6408-24-m.szyprowski@samsung.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | DRM: fix struct sg_table nents vs. orig_nents misuse | expand |
On Wed, May 13, 2020 at 6:33 AM Marek Szyprowski <m.szyprowski@samsung.com> wrote: > > 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> Reviewed-by: Eric Anholt <eric@anholt.net> _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
diff --git a/drivers/gpu/drm/v3d/v3d_mmu.c b/drivers/gpu/drm/v3d/v3d_mmu.c index 3b81ea2..175c257 100644 --- a/drivers/gpu/drm/v3d/v3d_mmu.c +++ b/drivers/gpu/drm/v3d/v3d_mmu.c @@ -90,19 +90,16 @@ void v3d_mmu_insert_ptes(struct v3d_bo *bo) struct v3d_dev *v3d = to_v3d_dev(shmem_obj->base.dev); u32 page = bo->node.start; u32 page_prot = V3D_PTE_WRITEABLE | V3D_PTE_VALID; - unsigned int count; - struct scatterlist *sgl; + struct sg_dma_page_iter dma_iter; - for_each_sg(shmem_obj->sgt->sgl, sgl, shmem_obj->sgt->nents, count) { - u32 page_address = sg_dma_address(sgl) >> V3D_MMU_PAGE_SHIFT; + for_each_sgtable_dma_page(shmem_obj->sgt, &dma_iter, 0) { + dma_addr_t dma_addr = sg_page_iter_dma_address(&dma_iter); + u32 page_address = dma_addr >> V3D_MMU_PAGE_SHIFT; u32 pte = page_prot | page_address; - u32 i; - BUG_ON(page_address + (sg_dma_len(sgl) >> V3D_MMU_PAGE_SHIFT) >= - BIT(24)); - - for (i = 0; i < sg_dma_len(sgl) >> V3D_MMU_PAGE_SHIFT; i++) - v3d->pt[page++] = pte + i; + BUILD_BUG_ON(V3D_MMU_PAGE_SHIFT != PAGE_SIZE); + BUG_ON(page_address + 1 >= BIT(24)); + v3d->pt[page++] = pte; } WARN_ON_ONCE(page - bo->node.start !=
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> --- For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents vs. orig_nents misuse' thread: https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@samsung.com/T/ --- drivers/gpu/drm/v3d/v3d_mmu.c | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) -- 1.9.1 _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel