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@samsung.com --- 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);