[PATCH v2 12/21] drm: tegra: 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/tegra/gem.c   | 25 +++++++++++++------------
 drivers/gpu/drm/tegra/plane.c | 13 +++++++------
 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index 6237681..5710ab4 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -98,8 +98,8 @@ static struct sg_table *tegra_bo_pin(struct device *dev, struct host1x_bo *bo,
 		 * the SG table needs to be copied to avoid overwriting any
 		 * other potential users of the original SG table.
 		 */
-		err = sg_alloc_table_from_sg(sgt, obj->sgt->sgl, obj->sgt->nents,
-					     GFP_KERNEL);
+		err = sg_alloc_table_from_sg(sgt, obj->sgt->sgl,
+					     obj->sgt->orig_nents, GFP_KERNEL);
 		if (err < 0)
 			goto free;
 	} else {
@@ -197,7 +197,7 @@ static int tegra_bo_iommu_map(struct tegra_drm *tegra, struct tegra_bo *bo)
 	bo->iova = bo->mm->start;
 
 	bo->size = iommu_map_sg(tegra->domain, bo->iova, bo->sgt->sgl,
-				bo->sgt->nents, prot);
+				bo->sgt->orig_nents, prot);
 	if (!bo->size) {
 		dev_err(tegra->drm->dev, "failed to map buffer\n");
 		err = -ENOMEM;
@@ -264,7 +264,7 @@ static struct tegra_bo *tegra_bo_alloc_object(struct drm_device *drm,
 static void tegra_bo_free(struct drm_device *drm, struct tegra_bo *bo)
 {
 	if (bo->pages) {
-		dma_unmap_sg(drm->dev, bo->sgt->sgl, bo->sgt->nents,
+		dma_unmap_sg(drm->dev, bo->sgt->sgl, bo->sgt->orig_nents,
 			     DMA_FROM_DEVICE);
 		drm_gem_put_pages(&bo->gem, bo->pages, true, true);
 		sg_free_table(bo->sgt);
@@ -290,9 +290,9 @@ static int tegra_bo_get_pages(struct drm_device *drm, struct tegra_bo *bo)
 		goto put_pages;
 	}
 
-	err = dma_map_sg(drm->dev, bo->sgt->sgl, bo->sgt->nents,
-			 DMA_FROM_DEVICE);
-	if (err == 0) {
+	bo->sgt->nents = dma_map_sg(drm->dev, bo->sgt->sgl, bo->sgt->orig_nents,
+				DMA_FROM_DEVICE);
+	if (bo->sgt->nents == 0) {
 		err = -EFAULT;
 		goto free_sgt;
 	}
@@ -571,7 +571,8 @@ int tegra_drm_mmap(struct file *file, struct vm_area_struct *vma)
 			goto free;
 	}
 
-	if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0)
+	sgt->nents = dma_map_sg(attach->dev, sgt->sgl, sgt->orig_nents, dir);
+	if (sgt->nents == 0)
 		goto free;
 
 	return sgt;
@@ -590,7 +591,7 @@ static void tegra_gem_prime_unmap_dma_buf(struct dma_buf_attachment *attach,
 	struct tegra_bo *bo = to_tegra_bo(gem);
 
 	if (bo->pages)
-		dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir);
+		dma_unmap_sg(attach->dev, sgt->sgl, sgt->orig_nents, dir);
 
 	sg_free_table(sgt);
 	kfree(sgt);
@@ -609,7 +610,7 @@ static int tegra_gem_prime_begin_cpu_access(struct dma_buf *buf,
 	struct drm_device *drm = gem->dev;
 
 	if (bo->pages)
-		dma_sync_sg_for_cpu(drm->dev, bo->sgt->sgl, bo->sgt->nents,
+		dma_sync_sg_for_cpu(drm->dev, bo->sgt->sgl, bo->sgt->orig_nents,
 				    DMA_FROM_DEVICE);
 
 	return 0;
@@ -623,8 +624,8 @@ static int tegra_gem_prime_end_cpu_access(struct dma_buf *buf,
 	struct drm_device *drm = gem->dev;
 
 	if (bo->pages)
-		dma_sync_sg_for_device(drm->dev, bo->sgt->sgl, bo->sgt->nents,
-				       DMA_TO_DEVICE);
+		dma_sync_sg_for_device(drm->dev, bo->sgt->sgl,
+				       bo->sgt->orig_nents, DMA_TO_DEVICE);
 
 	return 0;
 }
diff --git a/drivers/gpu/drm/tegra/plane.c b/drivers/gpu/drm/tegra/plane.c
index 9ccfb56..3982bf8 100644
--- a/drivers/gpu/drm/tegra/plane.c
+++ b/drivers/gpu/drm/tegra/plane.c
@@ -130,9 +130,10 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
 		}
 
 		if (sgt) {
-			err = dma_map_sg(dc->dev, sgt->sgl, sgt->nents,
-					 DMA_TO_DEVICE);
-			if (err == 0) {
+			sgt->nents = dma_map_sg(dc->dev, sgt->sgl,
+						sgt->orig_nents,
+						DMA_TO_DEVICE);
+			if (sgt->nents == 0) {
 				err = -ENOMEM;
 				goto unpin;
 			}
@@ -143,7 +144,7 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
 			 * map its SG table to a single contiguous chunk of
 			 * I/O virtual memory.
 			 */
-			if (err > 1) {
+			if (sgt->nents > 1) {
 				err = -EINVAL;
 				goto unpin;
 			}
@@ -165,7 +166,7 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
 		struct sg_table *sgt = state->sgt[i];
 
 		if (sgt)
-			dma_unmap_sg(dc->dev, sgt->sgl, sgt->nents,
+			dma_unmap_sg(dc->dev, sgt->sgl, sgt->orig_nents,
 				     DMA_TO_DEVICE);
 
 		host1x_bo_unpin(dc->dev, &bo->base, sgt);
@@ -185,7 +186,7 @@ static void tegra_dc_unpin(struct tegra_dc *dc, struct tegra_plane_state *state)
 		struct sg_table *sgt = state->sgt[i];
 
 		if (sgt)
-			dma_unmap_sg(dc->dev, sgt->sgl, sgt->nents,
+			dma_unmap_sg(dc->dev, sgt->sgl, sgt->orig_nents,
 				     DMA_TO_DEVICE);
 
 		host1x_bo_unpin(dc->dev, &bo->base, sgt);
-- 
1.9.1