Re: [RFC 10/17] drm: radeon: 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/radeon/radeon_ttm.c | 10 +++++-----
  1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
index 5d50c9e..4770880 100644
--- a/drivers/gpu/drm/radeon/radeon_ttm.c
+++ b/drivers/gpu/drm/radeon/radeon_ttm.c
@@ -481,7 +481,7 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt *ttm)
  {
  	struct radeon_device *rdev = radeon_get_rdev(ttm->bdev);
  	struct radeon_ttm_tt *gtt = (void *)ttm;
-	unsigned pinned = 0, nents;
+	unsigned pinned = 0;
  	int r;
int write = !(gtt->userflags & RADEON_GEM_USERPTR_READONLY);
@@ -522,8 +522,8 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt *ttm)
  		goto release_sg;
r = -ENOMEM;
-	nents = dma_map_sg(rdev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
-	if (nents == 0)
+	ttm->sg->nents = dma_map_sg(rdev->dev, ttm->sg->sgl,
+	if (ttm->sg->nents == 0)
  		goto release_sg;
drm_prime_sg_to_page_addr_arrays(ttm->sg, ttm->pages,
@@ -554,9 +554,9 @@ static void radeon_ttm_tt_unpin_userptr(struct ttm_tt *ttm)
  		return;
/* free the sg table and pages again */
-	dma_unmap_sg(rdev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
+	dma_unmap_sg(rdev->dev, ttm->sg->sgl, ttm->sg->orig_nents, direction);
- for_each_sg_page(ttm->sg->sgl, &sg_iter, ttm->sg->nents, 0) {
+	for_each_sg_page(ttm->sg->sgl, &sg_iter, ttm->sg->orig_nents, 0) {
  		struct page *page = sg_page_iter_page(&sg_iter);
  		if (!(gtt->userflags & RADEON_GEM_USERPTR_READONLY))
  			set_page_dirty(page);

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