Re: [RFC 02/17] drm: amdgpu: fix sg_table nents vs. orig_nents misuse

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Am 28.04.20 um 15:19 schrieb Marek Szyprowski:
The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the
numer of the created entries in the DMA address space. However the
subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be
called with the original number of entries passed to dma_map_sg. The
sg_table->nents in turn holds the result of the dma_map_sg call as stated
in include/linux/scatterlist.h. Adapt the code to obey those rules.

Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>

Reviewed-by: Christian König <christian.koenig@xxxxxxx>

---
  drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 7 ++++---
  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c     | 8 ++++----
  2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
index 43d8ed7..4df813e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
@@ -307,8 +307,9 @@ static struct sg_table *amdgpu_dma_buf_map(struct dma_buf_attachment *attach,
  		if (IS_ERR(sgt))
  			return sgt;
- if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
-				      DMA_ATTR_SKIP_CPU_SYNC))
+		sgt->nents = dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->orig_nents,
+					      dir, DMA_ATTR_SKIP_CPU_SYNC);
+		if (!sgt->nents)
  			goto error_free;
  		break;
@@ -349,7 +350,7 @@ static void amdgpu_dma_buf_unmap(struct dma_buf_attachment *attach,
  	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
if (sgt->sgl->page_link) {
-		dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir);
+		dma_unmap_sg(attach->dev, sgt->sgl, sgt->orig_nents, dir);
  		sg_free_table(sgt);
  		kfree(sgt);
  	} else {
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index d5543c2..5f31585 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1043,7 +1043,6 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
  {
  	struct amdgpu_device *adev = amdgpu_ttm_adev(ttm->bdev);
  	struct amdgpu_ttm_tt *gtt = (void *)ttm;
-	unsigned nents;
  	int r;
int write = !(gtt->userflags & AMDGPU_GEM_USERPTR_READONLY);
@@ -1059,8 +1058,9 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
/* Map SG to device */
  	r = -ENOMEM;
-	nents = dma_map_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
-	if (nents == 0)
+	ttm->sg->nents = dma_map_sg(adev->dev, ttm->sg->sgl,
+				    ttm->sg->orig_nents, direction);
+	if (ttm->sg->nents == 0)
  		goto release_sg;
/* convert SG to linear array of pages and dma addresses */
@@ -1091,7 +1091,7 @@ static void amdgpu_ttm_tt_unpin_userptr(struct ttm_tt *ttm)
  		return;
/* unmap the pages mapped to the device */
-	dma_unmap_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
+	dma_unmap_sg(adev->dev, ttm->sg->sgl, ttm->sg->orig_nents, direction);
sg_free_table(ttm->sg);

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