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 --- drivers/gpu/drm/v3d/v3d_mmu.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-)
diff --git a/drivers/gpu/drm/v3d/v3d_mmu.c b/drivers/gpu/drm/v3d/v3d_mmu.c index 3b81ea28c0bb..5a453532901f 100644 --- a/drivers/gpu/drm/v3d/v3d_mmu.c +++ b/drivers/gpu/drm/v3d/v3d_mmu.c @@ -90,18 +90,17 @@ 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) >= + BUG_ON(page_address + (PAGE_SIZE >> V3D_MMU_PAGE_SHIFT) >= BIT(24)); - - for (i = 0; i < sg_dma_len(sgl) >> V3D_MMU_PAGE_SHIFT; i++) + for (i = 0; i < PAGE_SIZE >> V3D_MMU_PAGE_SHIFT; i++) v3d->pt[page++] = pte + i; }