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>
---
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/etnaviv/etnaviv_gem.c | 12 +++++-------
drivers/gpu/drm/etnaviv/etnaviv_mmu.c | 13 +++----------
2 files changed, 8 insertions(+), 17 deletions(-)
diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
index dc9ef30..cc50c7b 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
@@ -27,7 +27,7 @@ static void etnaviv_gem_scatter_map(struct etnaviv_gem_object *etnaviv_obj)
* because display controller, GPU, etc. are not coherent.
*/
if (etnaviv_obj->flags & ETNA_BO_CACHE_MASK)
- dma_map_sg(dev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL);
+ dma_map_sgtable(dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
}
static void etnaviv_gem_scatterlist_unmap(struct etnaviv_gem_object *etnaviv_obj)
@@ -51,7 +51,7 @@ static void etnaviv_gem_scatterlist_unmap(struct etnaviv_gem_object *etnaviv_obj
* discard those writes.
*/
if (etnaviv_obj->flags & ETNA_BO_CACHE_MASK)
- dma_unmap_sg(dev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL);
+ dma_unmap_sgtable(dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
}
/* called with etnaviv_obj->lock held */
@@ -404,9 +404,8 @@ int etnaviv_gem_cpu_prep(struct drm_gem_object *obj, u32 op,
}
if (etnaviv_obj->flags & ETNA_BO_CACHED) {
- dma_sync_sg_for_cpu(dev->dev, etnaviv_obj->sgt->sgl,
- etnaviv_obj->sgt->nents,
- etnaviv_op_to_dma_dir(op));
+ dma_sync_sgtable_for_cpu(dev->dev, etnaviv_obj->sgt,
+ etnaviv_op_to_dma_dir(op));
etnaviv_obj->last_cpu_prep_op = op;
}
@@ -421,8 +420,7 @@ int etnaviv_gem_cpu_fini(struct drm_gem_object *obj)
if (etnaviv_obj->flags & ETNA_BO_CACHED) {
/* fini without a prep is almost certainly a userspace error */
WARN_ON(etnaviv_obj->last_cpu_prep_op == 0);
- dma_sync_sg_for_device(dev->dev, etnaviv_obj->sgt->sgl,
- etnaviv_obj->sgt->nents,
+ dma_sync_sgtable_for_device(dev->dev, etnaviv_obj->sgt,
etnaviv_op_to_dma_dir(etnaviv_obj->last_cpu_prep_op));
etnaviv_obj->last_cpu_prep_op = 0;
}
diff --git a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
index 3607d34..13b1005 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
@@ -79,7 +79,7 @@ static int etnaviv_iommu_map(struct etnaviv_iommu_context *context, u32 iova,
if (!context || !sgt)
return -EINVAL;
- for_each_sg(sgt->sgl, sg, sgt->nents, i) {
+ for_each_sgtable_dma_sg(sgt, sg, i) {
u32 pa = sg_dma_address(sg) - sg->offset;
size_t bytes = sg_dma_len(sg) + sg->offset;
@@ -95,14 +95,7 @@ static int etnaviv_iommu_map(struct etnaviv_iommu_context *context, u32 iova,
return 0;
fail:
- da = iova;
-
- for_each_sg(sgt->sgl, sg, i, j) {
- size_t bytes = sg_dma_len(sg) + sg->offset;
-
- etnaviv_context_unmap(context, da, bytes);
- da += bytes;
- }
+ etnaviv_context_unmap(context, iova, da - iova);
return ret;
}
@@ -113,7 +106,7 @@ static void etnaviv_iommu_unmap(struct etnaviv_iommu_context *context, u32 iova,
unsigned int da = iova;
int i;
- for_each_sg(sgt->sgl, sg, sgt->nents, i) {
+ for_each_sgtable_dma_sg(sgt, sg, i) {
size_t bytes = sg_dma_len(sg) + sg->offset;
etnaviv_context_unmap(context, da, bytes);
--
1.9.1
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