[PATCH v3 11/25] drm: radeon: fix common struct sg_table related issues

[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 the 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. A common mistake was to ignore a result
of the dma_map_sg function and don't use the sg_table->orig_nents at all.

To avoid such issues, lets use common dma-mapping wrappers operating
directly on the struct sg_table objects and adjust references to the
nents and orig_nents respectively.

Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
---
For more information, see '[PATCH v3 00/25] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/5/187
---
 drivers/gpu/drm/radeon/radeon_ttm.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
index 5d50c9e..166f84e 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);
@@ -521,9 +521,8 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt *ttm)
 	if (r)
 		goto release_sg;
 
-	r = -ENOMEM;
-	nents = dma_map_sg(rdev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
-	if (nents == 0)
+	r = dma_map_sgtable(rdev->dev, ttm->sg, direction);
+	if (r)
 		goto release_sg;
 
 	drm_prime_sg_to_page_addr_arrays(ttm->sg, ttm->pages,
@@ -554,9 +553,9 @@ 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_sgtable(rdev->dev, ttm->sg, 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);
-- 
1.9.1