diff mbox series

[v9,17/32] drm: rockchip: fix common struct sg_table related issues

Message ID 20200826063316.23486-18-m.szyprowski@samsung.com
State Superseded
Headers show
Series DRM: fix struct sg_table nents vs. orig_nents misuse | expand

Commit Message

Marek Szyprowski Aug. 26, 2020, 6:33 a.m. UTC
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.

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

---
 drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 23 +++++++++------------
 1 file changed, 10 insertions(+), 13 deletions(-)

-- 
2.17.1

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Comments

Robin Murphy Sept. 1, 2020, 8 p.m. UTC | #1
On 2020-08-26 07:33, 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.


Reviewed-by: Robin Murphy <robin.murphy@arm.com>


(Until now I hadn't noticed the crimes against the API that 
rockchip_gem_get_pages() is committing, but it's not this patch's 
fault... I'll have to take a closer look at that)

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

> ---

>   drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 23 +++++++++------------

>   1 file changed, 10 insertions(+), 13 deletions(-)

> 

> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c

> index 2970e534e2bb..cb50f2ba2e46 100644

> --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c

> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c

> @@ -36,8 +36,8 @@ static int rockchip_gem_iommu_map(struct rockchip_gem_object *rk_obj)

>   

>   	rk_obj->dma_addr = rk_obj->mm.start;

>   

> -	ret = iommu_map_sg(private->domain, rk_obj->dma_addr, rk_obj->sgt->sgl,

> -			   rk_obj->sgt->nents, prot);

> +	ret = iommu_map_sgtable(private->domain, rk_obj->dma_addr, rk_obj->sgt,

> +				prot);

>   	if (ret < rk_obj->base.size) {

>   		DRM_ERROR("failed to map buffer: size=%zd request_size=%zd\n",

>   			  ret, rk_obj->base.size);

> @@ -98,11 +98,10 @@ static int rockchip_gem_get_pages(struct rockchip_gem_object *rk_obj)

>   	 * TODO: Replace this by drm_clflush_sg() once it can be implemented

>   	 * without relying on symbols that are not exported.

>   	 */

> -	for_each_sg(rk_obj->sgt->sgl, s, rk_obj->sgt->nents, i)

> +	for_each_sgtable_sg(rk_obj->sgt, s, i)

>   		sg_dma_address(s) = sg_phys(s);

>   

> -	dma_sync_sg_for_device(drm->dev, rk_obj->sgt->sgl, rk_obj->sgt->nents,

> -			       DMA_TO_DEVICE);

> +	dma_sync_sgtable_for_device(drm->dev, rk_obj->sgt, DMA_TO_DEVICE);

>   

>   	return 0;

>   

> @@ -350,8 +349,8 @@ void rockchip_gem_free_object(struct drm_gem_object *obj)

>   		if (private->domain) {

>   			rockchip_gem_iommu_unmap(rk_obj);

>   		} else {

> -			dma_unmap_sg(drm->dev, rk_obj->sgt->sgl,

> -				     rk_obj->sgt->nents, DMA_BIDIRECTIONAL);

> +			dma_unmap_sgtable(drm->dev, rk_obj->sgt,

> +					  DMA_BIDIRECTIONAL, 0);

>   		}

>   		drm_prime_gem_destroy(obj, rk_obj->sgt);

>   	} else {

> @@ -476,15 +475,13 @@ rockchip_gem_dma_map_sg(struct drm_device *drm,

>   			struct sg_table *sg,

>   			struct rockchip_gem_object *rk_obj)

>   {

> -	int count = dma_map_sg(drm->dev, sg->sgl, sg->nents,

> -			       DMA_BIDIRECTIONAL);

> -	if (!count)

> -		return -EINVAL;

> +	int err = dma_map_sgtable(drm->dev, sg, DMA_BIDIRECTIONAL, 0);

> +	if (err)

> +		return err;

>   

>   	if (drm_prime_get_contiguous_size(sg) < attach->dmabuf->size) {

>   		DRM_ERROR("failed to map sg_table to contiguous linear address.\n");

> -		dma_unmap_sg(drm->dev, sg->sgl, sg->nents,

> -			     DMA_BIDIRECTIONAL);

> +		dma_unmap_sgtable(drm->dev, sg, DMA_BIDIRECTIONAL, 0);

>   		return -EINVAL;

>   	}

>   

> 

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diff mbox series

Patch

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
index 2970e534e2bb..cb50f2ba2e46 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
@@ -36,8 +36,8 @@  static int rockchip_gem_iommu_map(struct rockchip_gem_object *rk_obj)
 
 	rk_obj->dma_addr = rk_obj->mm.start;
 
-	ret = iommu_map_sg(private->domain, rk_obj->dma_addr, rk_obj->sgt->sgl,
-			   rk_obj->sgt->nents, prot);
+	ret = iommu_map_sgtable(private->domain, rk_obj->dma_addr, rk_obj->sgt,
+				prot);
 	if (ret < rk_obj->base.size) {
 		DRM_ERROR("failed to map buffer: size=%zd request_size=%zd\n",
 			  ret, rk_obj->base.size);
@@ -98,11 +98,10 @@  static int rockchip_gem_get_pages(struct rockchip_gem_object *rk_obj)
 	 * TODO: Replace this by drm_clflush_sg() once it can be implemented
 	 * without relying on symbols that are not exported.
 	 */
-	for_each_sg(rk_obj->sgt->sgl, s, rk_obj->sgt->nents, i)
+	for_each_sgtable_sg(rk_obj->sgt, s, i)
 		sg_dma_address(s) = sg_phys(s);
 
-	dma_sync_sg_for_device(drm->dev, rk_obj->sgt->sgl, rk_obj->sgt->nents,
-			       DMA_TO_DEVICE);
+	dma_sync_sgtable_for_device(drm->dev, rk_obj->sgt, DMA_TO_DEVICE);
 
 	return 0;
 
@@ -350,8 +349,8 @@  void rockchip_gem_free_object(struct drm_gem_object *obj)
 		if (private->domain) {
 			rockchip_gem_iommu_unmap(rk_obj);
 		} else {
-			dma_unmap_sg(drm->dev, rk_obj->sgt->sgl,
-				     rk_obj->sgt->nents, DMA_BIDIRECTIONAL);
+			dma_unmap_sgtable(drm->dev, rk_obj->sgt,
+					  DMA_BIDIRECTIONAL, 0);
 		}
 		drm_prime_gem_destroy(obj, rk_obj->sgt);
 	} else {
@@ -476,15 +475,13 @@  rockchip_gem_dma_map_sg(struct drm_device *drm,
 			struct sg_table *sg,
 			struct rockchip_gem_object *rk_obj)
 {
-	int count = dma_map_sg(drm->dev, sg->sgl, sg->nents,
-			       DMA_BIDIRECTIONAL);
-	if (!count)
-		return -EINVAL;
+	int err = dma_map_sgtable(drm->dev, sg, DMA_BIDIRECTIONAL, 0);
+	if (err)
+		return err;
 
 	if (drm_prime_get_contiguous_size(sg) < attach->dmabuf->size) {
 		DRM_ERROR("failed to map sg_table to contiguous linear address.\n");
-		dma_unmap_sg(drm->dev, sg->sgl, sg->nents,
-			     DMA_BIDIRECTIONAL);
+		dma_unmap_sgtable(drm->dev, sg, DMA_BIDIRECTIONAL, 0);
 		return -EINVAL;
 	}