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@xxxxxxxxxxx>
Reviewed-by: Steven Price <steven.price@xxxxxxx>
---
For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread:
https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@xxxxxxxxxxx/T/
---
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 b/drivers/gpu/drm/panfrost/panfrost_gem.c
index 17b654e..6696304 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 *obj)
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_BIDIRECTIONAL);
+ dma_unmap_sgtable(pfdev->dev, &bo->sgts[i],
+ DMA_BIDIRECTIONAL, 0);
sg_free_table(&bo->sgts[i]);
}
}
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index ed28aeb..eb2550e 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);
--
1.9.1
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