[v3,18/25] drm: rcar-du: fix common struct sg_table related issues

Message ID 20200505084614.30424-18-m.szyprowski@samsung.com
State New
Headers show
Series
  • DRM: fix struct sg_table nents vs. orig_nents misuse
Related show

Commit Message

Marek Szyprowski May 5, 2020, 8:46 a.m.
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 the 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. A common mistake was to ignore a result
of the dma_map_sg function and don't use the sg_table->orig_nents at all.

To avoid such issues, lets use common dma-mapping wrappers operating
directly on the struct sg_table objects and adjust references to the
nents and orig_nents respectively.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

---
For more information, see '[PATCH v3 00/25] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/5/187
---
 drivers/media/platform/vsp1/vsp1_drm.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

-- 
1.9.1

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Comments

Geert Uytterhoeven May 5, 2020, 9:24 a.m. | #1
Hi Marek,

On Tue, May 5, 2020 at 10:48 AM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
> 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 the 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. A common mistake was to ignore a result

> of the dma_map_sg function and don't use the sg_table->orig_nents at all.

>

> To avoid such issues, lets use common dma-mapping wrappers operating

> directly on the struct sg_table objects and adjust references to the

> nents and orig_nents respectively.

>

> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

> ---

> For more information, see '[PATCH v3 00/25] DRM: fix struct sg_table nents

> vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/5/187


For the modern lore-users:
https://lore.kernel.org/r/20200505083926.28503-1-m.szyprowski@samsung.com/

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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Patch

diff --git a/drivers/media/platform/vsp1/vsp1_drm.c b/drivers/media/platform/vsp1/vsp1_drm.c
index a4a45d6..8a2624b 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);
+	return dma_map_sgtable_attrs(vsp1->bus_master, sgt, DMA_TO_DEVICE,
+				     DMA_ATTR_SKIP_CPU_SYNC);
+	return sgt->nents;
 }
 EXPORT_SYMBOL_GPL(vsp1_du_map_sg);
 
@@ -921,8 +922,8 @@  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_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
+	dma_unmap_sgtable_attrs(vsp1->bus_master, sgt, DMA_TO_DEVICE,
+				DMA_ATTR_SKIP_CPU_SYNC);
 }
 EXPORT_SYMBOL_GPL(vsp1_du_unmap_sg);