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* [PATCH v7 28/36] dmabuf: fix common struct sg_table related issues
       [not found] ` <CGME20200619103712eucas1p1a29d1fe41061ed5b138a9cdd5d811419@eucas1p1.samsung.com>
@ 2020-06-19 10:36   ` Marek Szyprowski
  0 siblings, 0 replies; only message in thread
From: Marek Szyprowski @ 2020-06-19 10:36 UTC (permalink / raw)
  To: dri-devel, iommu, linaro-mm-sig, linux-kernel
  Cc: Marek Szyprowski, Christoph Hellwig, Robin Murphy,
	Bartlomiej Zolnierkiewicz, linux-arm-kernel, David Airlie,
	Daniel Vetter, Sumit Semwal, Gerd Hoffmann, linux-media

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()

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>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
 drivers/dma-buf/heaps/heap-helpers.c | 13 ++++++-------
 drivers/dma-buf/udmabuf.c            |  7 +++----
 2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/dma-buf/heaps/heap-helpers.c b/drivers/dma-buf/heaps/heap-helpers.c
index 9f964ca3f59c..d0696cf937af 100644
--- a/drivers/dma-buf/heaps/heap-helpers.c
+++ b/drivers/dma-buf/heaps/heap-helpers.c
@@ -140,13 +140,12 @@ struct sg_table *dma_heap_map_dma_buf(struct dma_buf_attachment *attachment,
 				      enum dma_data_direction direction)
 	struct dma_heaps_attachment *a = attachment->priv;
-	struct sg_table *table;
-	table = &a->table;
+	struct sg_table *table = &a->table;
+	int ret;
-	if (!dma_map_sg(attachment->dev, table->sgl, table->nents,
-			direction))
-		table = ERR_PTR(-ENOMEM);
+	ret = dma_map_sgtable(attachment->dev, table, direction, 0);
+	if (ret)
+		table = ERR_PTR(ret);
 	return table;
@@ -154,7 +153,7 @@ static void dma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
 				   struct sg_table *table,
 				   enum dma_data_direction direction)
-	dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
+	dma_unmap_sgtable(attachment->dev, table, direction, 0);
 static vm_fault_t dma_heap_vm_fault(struct vm_fault *vmf)
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index acb26c627d27..89e293bd9252 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -63,10 +63,9 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
 	if (ret < 0)
 		goto err;
-	if (!dma_map_sg(dev, sg->sgl, sg->nents, direction)) {
-		ret = -EINVAL;
+	ret = dma_map_sgtable(dev, sg, direction, 0);
+	if (ret < 0)
 		goto err;
-	}
 	return sg;
@@ -78,7 +77,7 @@ static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
 static void put_sg_table(struct device *dev, struct sg_table *sg,
 			 enum dma_data_direction direction)
-	dma_unmap_sg(dev, sg->sgl, sg->nents, direction);
+	dma_unmap_sgtable(dev, sg, direction, 0);

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     [not found] <20200619103636.11974-1-m.szyprowski@samsung.com>
     [not found] ` <CGME20200619103712eucas1p1a29d1fe41061ed5b138a9cdd5d811419@eucas1p1.samsung.com>
2020-06-19 10:36   ` [PATCH v7 28/36] dmabuf: fix common struct sg_table related issues Marek Szyprowski

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