[RFC v3 11/14] vb2: dma-contig: Add WARN_ON_ONCE() to check for potential bugs

[Sakari Ailus]

The scatterlist should always be present when the cache would need to be
flushed. Each buffer type has its own means to provide that. Add
WARN_ON_ONCE() to check the scatterist exists.

Signed-off-by: Sakari Ailus <sakari.ailus at linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil at cisco.com>
---
 drivers/media/v4l2-core/videobuf2-dma-contig.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
index 6a707d3..2847fbf 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
@@ -120,7 +120,7 @@ static void vb2_dc_prepare(void *buf_priv)
 	 * DMABUF exporter will flush the cache for us; only USERPTR
 	 * and MMAP buffers with non-coherent memory will be flushed.
 	 */
-	if (buf->attrs & DMA_ATTR_NON_CONSISTENT)
+	if (buf->attrs & DMA_ATTR_NON_CONSISTENT && !WARN_ON_ONCE(!sgt))
 		dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->orig_nents,
 				       buf->dma_dir);
 }
@@ -134,7 +134,7 @@ static void vb2_dc_finish(void *buf_priv)
 	 * DMABUF exporter will flush the cache for us; only USERPTR
 	 * and MMAP buffers with non-coherent memory will be flushed.
 	 */
-	if (buf->attrs & DMA_ATTR_NON_CONSISTENT)
+	if (buf->attrs & DMA_ATTR_NON_CONSISTENT && !WARN_ON_ONCE(!sgt))
 		dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->orig_nents,
 				    buf->dma_dir);
 }
@@ -380,7 +380,7 @@ static int vb2_dc_dmabuf_ops_begin_cpu_access(struct dma_buf *dbuf,
 	 * DMABUF exporter will flush the cache for us; only USERPTR
 	 * and MMAP buffers with non-coherent memory will be flushed.
 	 */
-	if (buf->attrs & DMA_ATTR_NON_CONSISTENT)
+	if (buf->attrs & DMA_ATTR_NON_CONSISTENT && !WARN_ON_ONCE(!sgt))
 		dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->nents,
 				    buf->dma_dir);
 
@@ -397,7 +397,7 @@ static int vb2_dc_dmabuf_ops_end_cpu_access(struct dma_buf *dbuf,
 	 * DMABUF exporter will flush the cache for us; only USERPTR
 	 * and MMAP buffers with non-coherent memory will be flushed.
 	 */
-	if (buf->attrs & DMA_ATTR_NON_CONSISTENT)
+	if (buf->attrs & DMA_ATTR_NON_CONSISTENT && !WARN_ON_ONCE(!sgt))
 		dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->nents,
 				       buf->dma_dir);
 
-- 
2.7.4