Commit efcb3730 authored by Marek Szyprowski's avatar Marek Szyprowski
Browse files

drm: armada: 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>
parent 6c6fa39c

drivers/gpu/drm/armada/armada_gem.c

+11 −13
Original line number Diff line number Diff line
@@ -379,7 +379,7 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, 
	struct armada_gem_object *dobj = drm_to_armada_gem(obj);

	struct scatterlist *sg;

	struct sg_table *sgt;

	int i, num;

	int i;



	sgt = kmalloc(sizeof(*sgt), GFP_KERNEL);

	if (!sgt)
@@ -395,22 +395,18 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, 


		mapping = dobj->obj.filp->f_mapping;



		for_each_sg(sgt->sgl, sg, count, i) {

		for_each_sgtable_sg(sgt, sg, i) {

			struct page *page;



			page = shmem_read_mapping_page(mapping, i);

			if (IS_ERR(page)) {

				num = i;

			if (IS_ERR(page))

				goto release;

			}



			sg_set_page(sg, page, PAGE_SIZE, 0);

		}



		if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0) {

			num = sgt->nents;

		if (dma_map_sgtable(attach->dev, sgt, dir, 0))

			goto release;

		}

	} else if (dobj->page) {

		/* Single contiguous page */

		if (sg_alloc_table(sgt, 1, GFP_KERNEL))
@@ -418,7 +414,7 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, 


		sg_set_page(sgt->sgl, dobj->page, dobj->obj.size, 0);



		if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0)

		if (dma_map_sgtable(attach->dev, sgt, dir, 0))

			goto free_table;

	} else if (dobj->linear) {

		/* Single contiguous physical region - no struct page */
@@ -432,7 +428,8 @@ armada_gem_prime_map_dma_buf(struct dma_buf_attachment *attach, 
	return sgt;



 release:

	for_each_sg(sgt->sgl, sg, num, i)

	for_each_sgtable_sg(sgt, sg, i)

		if (sg_page(sg))

			put_page(sg_page(sg));

 free_table:

	sg_free_table(sgt);
@@ -449,11 +446,12 @@ static void armada_gem_prime_unmap_dma_buf(struct dma_buf_attachment *attach, 
	int i;



	if (!dobj->linear)

		dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir);

		dma_unmap_sgtable(attach->dev, sgt, dir, 0);



	if (dobj->obj.filp) {

		struct scatterlist *sg;

		for_each_sg(sgt->sgl, sg, sgt->nents, i)



		for_each_sgtable_sg(sgt, sg, i)

			put_page(sg_page(sg));

	}

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