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.szyprow...@samsung.com>
---
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

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