[RFC 01/17] drm: core: fix sg_table nents vs. orig_nents misuse

[Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>]

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>
---
 drivers/gpu/drm/drm_cache.c            | 2 +-
 drivers/gpu/drm/drm_gem_shmem_helper.c | 7 ++++---
 drivers/gpu/drm/drm_prime.c            | 9 +++++----
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
index 03e01b0..63bd497 100644
--- a/drivers/gpu/drm/drm_cache.c
+++ b/drivers/gpu/drm/drm_cache.c
@@ -127,7 +127,7 @@ static void drm_cache_flush_clflush(struct page *pages[],
 		struct sg_page_iter sg_iter;
 
 		mb(); /*CLFLUSH is ordered only by using memory barriers*/
-		for_each_sg_page(st->sgl, &sg_iter, st->nents, 0)
+		for_each_sg_page(st->sgl, &sg_iter, st->orig_nents, 0)
 			drm_clflush_page(sg_page_iter_page(&sg_iter));
 		mb(); /*Make sure that all cache line entry is flushed*/
 
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index df31e57..f47caa7 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -118,7 +118,7 @@ void drm_gem_shmem_free_object(struct drm_gem_object *obj)
 	} else {
 		if (shmem->sgt) {
 			dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
-				     shmem->sgt->nents, DMA_BIDIRECTIONAL);
+				     shmem->sgt->orig_nents, DMA_BIDIRECTIONAL);
 			sg_free_table(shmem->sgt);
 			kfree(shmem->sgt);
 		}
@@ -396,7 +396,7 @@ void drm_gem_shmem_purge_locked(struct drm_gem_object *obj)
 	WARN_ON(!drm_gem_shmem_is_purgeable(shmem));
 
 	dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
-		     shmem->sgt->nents, DMA_BIDIRECTIONAL);
+		     shmem->sgt->orig_nents, DMA_BIDIRECTIONAL);
 	sg_free_table(shmem->sgt);
 	kfree(shmem->sgt);
 	shmem->sgt = NULL;
@@ -623,7 +623,8 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_object *obj)
 		goto err_put_pages;
 	}
 	/* Map the pages for use by the h/w. */
-	dma_map_sg(obj->dev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL);
+	sgt->nents = dma_map_sg(obj->dev->dev, sgt->sgl, sgt->orig_nents,
+				DMA_BIDIRECTIONAL);
 
 	shmem->sgt = sgt;
 
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 282774e..f3e2d2a 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -626,8 +626,9 @@ struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
 	else
 		sgt = obj->dev->driver->gem_prime_get_sg_table(obj);
 
-	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) {
 		sg_free_table(sgt);
 		kfree(sgt);
 		sgt = ERR_PTR(-ENOMEM);
@@ -652,7 +653,7 @@ void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
 	if (!sgt)
 		return;
 
-	dma_unmap_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
+	dma_unmap_sg_attrs(attach->dev, sgt->sgl, sgt->orig_nents, dir,
 			   DMA_ATTR_SKIP_CPU_SYNC);
 	sg_free_table(sgt);
 	kfree(sgt);
@@ -975,7 +976,7 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
 	 */
 	page_index = 0;
 	dma_index = 0;
-	for_each_sg(sgt->sgl, sg, sgt->nents, count) {
+	for_each_sg(sgt->sgl, sg, sgt->orig_nents, count) {
 		page_len = sg->length;
 		page = sg_page(sg);
 		dma_len = sg_dma_len(sg);
-- 
1.9.1

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