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()

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 <>
Reviewed-by: Steven Price <>
Reviewed-by: Rob Herring <>
 drivers/gpu/drm/panfrost/panfrost_gem.c | 4 ++--
 drivers/gpu/drm/panfrost/panfrost_mmu.c | 7 +++----
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c 
index ac5d0aa80276..ba8450ea04d0 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
@@ -41,8 +41,8 @@ static void panfrost_gem_free_object(struct drm_gem_object 
                for (i = 0; i < n_sgt; i++) {
                        if (bo->sgts[i].sgl) {
-                               dma_unmap_sg(pfdev->dev, bo->sgts[i].sgl,
-                                            bo->sgts[i].nents, 
+                               dma_unmap_sgtable(pfdev->dev, &bo->sgts[i],
+                                                 DMA_BIDIRECTIONAL, 0);
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c 
index 0a339c6fbfaa..fd294f6a7d3b 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -253,7 +253,7 @@ static int mmu_map_sg(struct panfrost_device *pfdev, struct 
panfrost_mmu *mmu,
        struct io_pgtable_ops *ops = mmu->pgtbl_ops;
        u64 start_iova = iova;
-       for_each_sg(sgt->sgl, sgl, sgt->nents, count) {
+       for_each_sgtable_dma_sg(sgt, sgl, count) {
                unsigned long paddr = sg_dma_address(sgl);
                size_t len = sg_dma_len(sgl);
@@ -517,10 +517,9 @@ static int panfrost_mmu_map_fault_addr(struct 
panfrost_device *pfdev, int as,
        if (ret)
                goto err_pages;
-       if (!dma_map_sg(pfdev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL)) {
-               ret = -EINVAL;
+       ret = dma_map_sgtable(pfdev->dev, sgt, DMA_BIDIRECTIONAL, 0);
+       if (ret)
                goto err_map;
-       }
        mmu_map_sg(pfdev, bomapping->mmu, addr,
                   IOMMU_WRITE | IOMMU_READ | IOMMU_NOEXEC, sgt);

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