On 2020-08-26 07:33, Marek Szyprowski wrote:
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.
Reviewed-by: Robin Murphy robin.murphy@arm.com
Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com
drivers/gpu/drm/tegra/gem.c | 27 ++++++++++----------------- drivers/gpu/drm/tegra/plane.c | 15 +++++---------- 2 files changed, 15 insertions(+), 27 deletions(-)
diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c index 723df142a981..01d94befab11 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);@@ -196,8 +196,7 @@ 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->size = iommu_map_sgtable(tegra->domain, bo->iova, bo->sgt, prot); if (!bo->size) { dev_err(tegra->drm->dev, "failed to map buffer\n"); err = -ENOMEM;
@@ -264,8 +263,7 @@ 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_FROM_DEVICE);
dma_unmap_sgtable(drm->dev, bo->sgt, DMA_FROM_DEVICE, 0);@@ -290,12 +288,9 @@ 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) {
err = -EFAULT;
- err = dma_map_sgtable(drm->dev, bo->sgt, DMA_FROM_DEVICE, 0);
- if (err) goto free_sgt;
- }
return 0; @@ -571,7 +566,7 @@ tegra_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, goto free; }
- if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0)
- if (dma_map_sgtable(attach->dev, sgt, dir, 0)) goto free;
return sgt; @@ -590,7 +585,7 @@ 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_sgtable(attach->dev, sgt, dir, 0);sg_free_table(sgt); kfree(sgt); @@ -609,8 +604,7 @@ 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_FROM_DEVICE);
dma_sync_sgtable_for_cpu(drm->dev, bo->sgt, DMA_FROM_DEVICE);return 0; } @@ -623,8 +617,7 @@ 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_sgtable_for_device(drm->dev, bo->sgt, DMA_TO_DEVICE);return 0; } diff --git a/drivers/gpu/drm/tegra/plane.c b/drivers/gpu/drm/tegra/plane.c index 4cd0461cc508..539d14935728 100644 --- a/drivers/gpu/drm/tegra/plane.c +++ b/drivers/gpu/drm/tegra/plane.c @@ -131,12 +131,9 @@ 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) {err = -ENOMEM;
err = dma_map_sgtable(dc->dev, sgt, DMA_TO_DEVICE, 0);if (err) goto unpin;
}/* * The display controller needs contiguous memory, so @@ -144,7 +141,7 @@ 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; }@@ -166,8 +163,7 @@ 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_TO_DEVICE);
dma_unmap_sgtable(dc->dev, sgt, DMA_TO_DEVICE, 0);host1x_bo_unpin(dc->dev, &bo->base, sgt); state->iova[i] = DMA_MAPPING_ERROR; @@ -186,8 +182,7 @@ 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_TO_DEVICE);
dma_unmap_sgtable(dc->dev, sgt, DMA_TO_DEVICE, 0);host1x_bo_unpin(dc->dev, &bo->base, sgt); state->iova[i] = DMA_MAPPING_ERROR;