[v5,29/38] drm: rcar-du: fix common struct sg_table related issues

Message ID 20200513133245.6408-29-m.szyprowski@samsung.com
State Superseded
Headers show
Series
  • DRM: fix struct sg_table nents vs. orig_nents misuse
Related show

Commit Message

Marek Szyprowski May 13, 2020, 1:32 p.m.
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.

dma_map_sgtable() function returns zero or an error code, so adjust the
return value check for the vsp1_du_map_sg() function.

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

---
For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread:
https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@samsung.com/T/
---
 drivers/gpu/drm/rcar-du/rcar_du_vsp.c  | 3 +--
 drivers/media/platform/vsp1/vsp1_drm.c | 8 ++++----
 2 files changed, 5 insertions(+), 6 deletions(-)

-- 
1.9.1

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Comments

Laurent Pinchart May 13, 2020, 2:23 p.m. | #1
Hi Marek,

Thank you for the patch.

On Wed, May 13, 2020 at 03:32:36PM +0200, Marek Szyprowski wrote:
> 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.

> 

> dma_map_sgtable() function returns zero or an error code, so adjust the

> return value check for the vsp1_du_map_sg() function.

> 

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


This is a very nice simplification, I've always foudn the dma_map_sg API
cumbersome to use.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>


I assume you will get the whole series merged in one go. If I need to
pick the patch up at any point, please let me know. Otherwise I'll wait
until I see it upstream, no reply needed :-)

> ---

> For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents

> vs. orig_nents misuse' thread:

> https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@samsung.com/T/

> ---

>  drivers/gpu/drm/rcar-du/rcar_du_vsp.c  | 3 +--

>  drivers/media/platform/vsp1/vsp1_drm.c | 8 ++++----

>  2 files changed, 5 insertions(+), 6 deletions(-)

> 

> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c

> index 5e4faf2..2fc1816 100644

> --- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c

> +++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c

> @@ -197,9 +197,8 @@ int rcar_du_vsp_map_fb(struct rcar_du_vsp *vsp, struct drm_framebuffer *fb,

>  			goto fail;

>  

>  		ret = vsp1_du_map_sg(vsp->vsp, sgt);

> -		if (!ret) {

> +		if (ret) {

>  			sg_free_table(sgt);

> -			ret = -ENOMEM;

>  			goto fail;

>  		}

>  	}

> diff --git a/drivers/media/platform/vsp1/vsp1_drm.c b/drivers/media/platform/vsp1/vsp1_drm.c

> index a4a45d6..86d5e3f 100644

> --- a/drivers/media/platform/vsp1/vsp1_drm.c

> +++ b/drivers/media/platform/vsp1/vsp1_drm.c

> @@ -912,8 +912,8 @@ 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(vsp1->bus_master, sgt, DMA_TO_DEVICE,

> +			       DMA_ATTR_SKIP_CPU_SYNC);

>  }

>  EXPORT_SYMBOL_GPL(vsp1_du_map_sg);

>  

> @@ -921,8 +921,8 @@ 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(vsp1->bus_master, sgt, DMA_TO_DEVICE,

> +			  DMA_ATTR_SKIP_CPU_SYNC);

>  }

>  EXPORT_SYMBOL_GPL(vsp1_du_unmap_sg);

>  


-- 
Regards,

Laurent Pinchart
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Patch

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
index 5e4faf2..2fc1816 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
@@ -197,9 +197,8 @@  int rcar_du_vsp_map_fb(struct rcar_du_vsp *vsp, struct drm_framebuffer *fb,
 			goto fail;
 
 		ret = vsp1_du_map_sg(vsp->vsp, sgt);
-		if (!ret) {
+		if (ret) {
 			sg_free_table(sgt);
-			ret = -ENOMEM;
 			goto fail;
 		}
 	}
diff --git a/drivers/media/platform/vsp1/vsp1_drm.c b/drivers/media/platform/vsp1/vsp1_drm.c
index a4a45d6..86d5e3f 100644
--- a/drivers/media/platform/vsp1/vsp1_drm.c
+++ b/drivers/media/platform/vsp1/vsp1_drm.c
@@ -912,8 +912,8 @@  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(vsp1->bus_master, sgt, DMA_TO_DEVICE,
+			       DMA_ATTR_SKIP_CPU_SYNC);
 }
 EXPORT_SYMBOL_GPL(vsp1_du_map_sg);
 
@@ -921,8 +921,8 @@  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(vsp1->bus_master, sgt, DMA_TO_DEVICE,
+			  DMA_ATTR_SKIP_CPU_SYNC);
 }
 EXPORT_SYMBOL_GPL(vsp1_du_unmap_sg);