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Subject[PATCH v10 16/30] drm: rockchip: fix common struct sg_table related issues
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: Robin Murphy <>
drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 23 +++++++++------------
1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
index 2970e534e2bb..cb50f2ba2e46 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
@@ -36,8 +36,8 @@ 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);
+ ret = iommu_map_sgtable(private->domain, rk_obj->dma_addr, rk_obj->sgt,
+ 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 +98,10 @@ 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_sgtable_sg(rk_obj->sgt, s, i)
sg_dma_address(s) = sg_phys(s);

- dma_sync_sg_for_device(drm->dev, rk_obj->sgt->sgl, rk_obj->sgt->nents,
+ dma_sync_sgtable_for_device(drm->dev, rk_obj->sgt, DMA_TO_DEVICE);

return 0;

@@ -350,8 +349,8 @@ void rockchip_gem_free_object(struct drm_gem_object *obj)
if (private->domain) {
} else {
- dma_unmap_sg(drm->dev, rk_obj->sgt->sgl,
- rk_obj->sgt->nents, DMA_BIDIRECTIONAL);
+ dma_unmap_sgtable(drm->dev, rk_obj->sgt,
drm_prime_gem_destroy(obj, rk_obj->sgt);
} else {
@@ -476,15 +475,13 @@ rockchip_gem_dma_map_sg(struct drm_device *drm,
struct sg_table *sg,
struct rockchip_gem_object *rk_obj)
- int count = dma_map_sg(drm->dev, sg->sgl, sg->nents,
- if (!count)
- return -EINVAL;
+ int err = dma_map_sgtable(drm->dev, sg, DMA_BIDIRECTIONAL, 0);
+ if (err)
+ return err;

if (drm_prime_get_contiguous_size(sg) < 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_sgtable(drm->dev, sg, DMA_BIDIRECTIONAL, 0);
return -EINVAL;

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