[PATCH v2 11/21] drm: rockchip: fix sg_table nents vs. orig_nents misuse

[Marek Szyprowski]

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 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. Adapt the code to obey those rules.

Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
---
For more information, see '[PATCH v2 00/21] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/4/373
---
 drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
index 0d18846..a024c71 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
@@ -37,7 +37,7 @@ 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);
+			   rk_obj->sgt->orig_nents, 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 +98,11 @@ 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_sg_for_device(drm->dev, rk_obj->sgt->sgl,
+			       rk_obj->sgt->orig_nents, DMA_TO_DEVICE);
 
 	return 0;
 
@@ -351,7 +351,8 @@ void rockchip_gem_free_object(struct drm_gem_object *obj)
 			rockchip_gem_iommu_unmap(rk_obj);
 		} else {
 			dma_unmap_sg(drm->dev, rk_obj->sgt->sgl,
-				     rk_obj->sgt->nents, DMA_BIDIRECTIONAL);
+				     rk_obj->sgt->orig_nents,
+				     DMA_BIDIRECTIONAL);
 		}
 		drm_prime_gem_destroy(obj, rk_obj->sgt);
 	} else {
@@ -493,14 +494,14 @@ 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,
+	int count = dma_map_sg(drm->dev, sg->sgl, sg->orig_nents,
 			       DMA_BIDIRECTIONAL);
 	if (!count)
 		return -EINVAL;
 
 	if (rockchip_sg_get_contiguous_size(sg, count) < 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_unmap_sg(drm->dev, sg->sgl, sg->orig_nents,
 			     DMA_BIDIRECTIONAL);
 		return -EINVAL;
 	}
-- 
1.9.1