Commit 6c6fa39c authored by Marek Szyprowski's avatar Marek Szyprowski
Browse files

drm: core: fix common struct sg_table related issues 



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: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: default avatarAndrzej Hajda <a.hajda@samsung.com>
Reviewed-by: default avatarRobin Murphy <robin.murphy@arm.com>
parent 0552daac

drivers/gpu/drm/drm_cache.c

+1 −1
Original line number Diff line number Diff line
@@ -127,7 +127,7 @@ drm_clflush_sg(struct sg_table *st) 
		struct sg_page_iter sg_iter;



		mb(); /*CLFLUSH is ordered only by using memory barriers*/

		for_each_sg_page(st->sgl, &sg_iter, st->nents, 0)

		for_each_sgtable_page(st, &sg_iter, 0)

			drm_clflush_page(sg_page_iter_page(&sg_iter));

		mb(); /*Make sure that all cache line entry is flushed*/

drivers/gpu/drm/drm_gem_shmem_helper.c

+9 −5
Original line number Diff line number Diff line
@@ -126,8 +126,8 @@ void drm_gem_shmem_free_object(struct drm_gem_object *obj) 
		drm_prime_gem_destroy(obj, shmem->sgt);

	} else {

		if (shmem->sgt) {

			dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,

				     shmem->sgt->nents, DMA_BIDIRECTIONAL);

			dma_unmap_sgtable(obj->dev->dev, shmem->sgt,

					  DMA_BIDIRECTIONAL, 0);

			sg_free_table(shmem->sgt);

			kfree(shmem->sgt);

		}
@@ -424,8 +424,7 @@ void drm_gem_shmem_purge_locked(struct drm_gem_object *obj) 


	WARN_ON(!drm_gem_shmem_is_purgeable(shmem));



	dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,

		     shmem->sgt->nents, DMA_BIDIRECTIONAL);

	dma_unmap_sgtable(obj->dev->dev, shmem->sgt, DMA_BIDIRECTIONAL, 0);

	sg_free_table(shmem->sgt);

	kfree(shmem->sgt);

	shmem->sgt = NULL;
@@ -697,12 +696,17 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_object *obj) 
		goto err_put_pages;

	}

	/* Map the pages for use by the h/w. */

	dma_map_sg(obj->dev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL);

	ret = dma_map_sgtable(obj->dev->dev, sgt, DMA_BIDIRECTIONAL, 0);

	if (ret)

		goto err_free_sgt;



	shmem->sgt = sgt;



	return sgt;



err_free_sgt:

	sg_free_table(sgt);

	kfree(sgt);

err_put_pages:

	drm_gem_shmem_put_pages(shmem);

	return ERR_PTR(ret);

drivers/gpu/drm/drm_prime.c

+6 −5
Original line number Diff line number Diff line
@@ -617,6 +617,7 @@ struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach, 
{

	struct drm_gem_object *obj = attach->dmabuf->priv;

	struct sg_table *sgt;

	int ret;



	if (WARN_ON(dir == DMA_NONE))

		return ERR_PTR(-EINVAL);
@@ -626,11 +627,12 @@ struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach, 
	else

		sgt = obj->dev->driver->gem_prime_get_sg_table(obj);



	if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,

			      DMA_ATTR_SKIP_CPU_SYNC)) {

	ret = dma_map_sgtable(attach->dev, sgt, dir,

			      DMA_ATTR_SKIP_CPU_SYNC);

	if (ret) {

		sg_free_table(sgt);

		kfree(sgt);

		sgt = ERR_PTR(-ENOMEM);

		sgt = ERR_PTR(ret);

	}



	return sgt;
@@ -652,8 +654,7 @@ void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach, 
	if (!sgt)

		return;



	dma_unmap_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,

			   DMA_ATTR_SKIP_CPU_SYNC);

	dma_unmap_sgtable(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC);

	sg_free_table(sgt);

	kfree(sgt);

}

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