[PATCH v2 17/21] drm: rcar-du: fix sg_table nents vs. orig_nents misuse

[PATCH v2 17/21] drm: rcar-du: fix sg_table nents vs. orig_nents misuse

[Marek Szyprowski]

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@samsung.com>
---
For more information, see '[PATCH v2 00/21] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/4/373
---
 drivers/media/platform/vsp1/vsp1_drm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/media/platform/vsp1/vsp1_drm.c b/drivers/media/platform/vsp1/vsp1_drm.c
index a4a45d6..b54a30f 100644
--- a/drivers/media/platform/vsp1/vsp1_drm.c
+++ b/drivers/media/platform/vsp1/vsp1_drm.c
@@ -912,8 +912,9 @@ int vsp1_du_map_sg(struct device *dev, struct sg_table *sgt)
 	 * skip cache sync. This will need to be revisited when support for
 	 * non-coherent buffers will be added to the DU driver.
 	 */
-	return dma_map_sg_attrs(vsp1->bus_master, sgt->sgl, sgt->nents,
-				DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
+	sgt->nents = dma_map_sg_attrs(vsp1->bus_master, sgt->sgl,
+			sgt->orig_nents, DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
+	return sgt->nents;
 }
 EXPORT_SYMBOL_GPL(vsp1_du_map_sg);
 
@@ -921,7 +922,7 @@ void vsp1_du_unmap_sg(struct device *dev, struct sg_table *sgt)
 {
 	struct vsp1_device *vsp1 = dev_get_drvdata(dev);
 
-	dma_unmap_sg_attrs(vsp1->bus_master, sgt->sgl, sgt->nents,
+	dma_unmap_sg_attrs(vsp1->bus_master, sgt->sgl, sgt->orig_nents,
 			   DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
 }
 EXPORT_SYMBOL_GPL(vsp1_du_unmap_sg);
-- 
1.9.1