The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().

struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()
function.

To avoid such issues, lets use a common dma-mapping wrappers operating
directly on the struct sg_table objects and use scatterlist page
iterators where possible. This, almost always, hides references to the
nents and orig_nents entries, making the code robust, easier to follow
and copy/paste safe.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Andrzej Hajda <redacted>
---
  drivers/gpu/drm/drm_cache.c            |  2 +-
  drivers/gpu/drm/drm_gem_shmem_helper.c | 14 +++++++++-----
  drivers/gpu/drm/drm_prime.c            | 11 ++++++-----
  3 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
index 03e01b000f7a..0fe3c496002a 100644
--- a/drivers/gpu/drm/drm_cache.c
+++ b/drivers/gpu/drm/drm_cache.c

@@ -127,7 +127,7 @@ drm_clflush_sg(struct sg_table *st)
  		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_sgtable_page(st, &sg_iter, 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 4b7cfbac4daa..47d8211221f2 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -126,8 +126,8 @@ void drm_gem_shmem_free_object(struct drm_gem_object *obj)
  		drm_prime_gem_destroy(obj, shmem->sgt);
  	} else {
  		if (shmem->sgt) {
-			dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
-				     shmem->sgt->nents, DMA_BIDIRECTIONAL);
+			dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
+					  DMA_BIDIRECTIONAL, 0);
  			sg_free_table(shmem->sgt);
  			kfree(shmem->sgt);
  		}

@@ -424,8 +424,7 @@ 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);
+	dma_unmap_sgtable(obj->dev->dev, shmem->sgt, DMA_BIDIRECTIONAL, 0);
  	sg_free_table(shmem->sgt);
  	kfree(shmem->sgt);
  	shmem->sgt = NULL;

@@ -697,12 +696,17 @@ 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);
+	ret = dma_map_sgtable(obj->dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
+	if (ret)
+		goto err_free_sgt;
  
  	shmem->sgt = sgt;
  
  	return sgt;
  
+err_free_sgt:
+	sg_free_table(sgt);
+	kfree(sgt);

  err_put_pages:
  	drm_gem_shmem_put_pages(shmem);
  	return ERR_PTR(ret);

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 5d181bf60a44..c45b0cc6e31d 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c

@@ -617,6 +617,7 @@ struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
  {
  	struct drm_gem_object *obj = attach->dmabuf->priv;
  	struct sg_table *sgt;
+	int ret;
  
  	if (WARN_ON(dir == DMA_NONE))
  		return ERR_PTR(-EINVAL);

@@ -626,11 +627,12 @@ 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)) {
+	ret = dma_map_sgtable(attach->dev, sgt, dir,
+			      DMA_ATTR_SKIP_CPU_SYNC);
+	if (ret) {
  		sg_free_table(sgt);
  		kfree(sgt);
-		sgt = ERR_PTR(-ENOMEM);
+		sgt = ERR_PTR(ret);
  	}
  
  	return sgt;

@@ -652,8 +654,7 @@ 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_ATTR_SKIP_CPU_SYNC);
+	dma_unmap_sgtable(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC);
  	sg_free_table(sgt);
  	kfree(sgt);
  }