dmabuf: fix common struct sg_table related issues (62296b39) · Commits · 戴 / test

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> Acked-by:

Gerd Hoffmann <kraxel@redhat.com>

drivers/dma-buf/heaps/heap-helpers.c

+6 −7

Original line number	Diff line number	Diff line
		@@ -140,13 +140,12 @@ struct sg_table dma_heap_map_dma_buf(struct dma_buf_attachment attachment,
		enum dma_data_direction direction)
		{
		struct dma_heaps_attachment *a = attachment->priv;
		struct sg_table *table;

		table = &a->table;
		struct sg_table *table = &a->table;
		int ret;

		if (!dma_map_sg(attachment->dev, table->sgl, table->nents,
		direction))
		table = ERR_PTR(-ENOMEM);
		ret = dma_map_sgtable(attachment->dev, table, direction, 0);
		if (ret)
		table = ERR_PTR(ret);
		return table;
		}

		@@ -154,7 +153,7 @@ static void dma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
		struct sg_table *table,
		enum dma_data_direction direction)
		{
		dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
		dma_unmap_sgtable(attachment->dev, table, direction, 0);
		}

		static vm_fault_t dma_heap_vm_fault(struct vm_fault *vmf)

drivers/dma-buf/udmabuf.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -63,10 +63,9 @@ static struct sg_table get_sg_table(struct device dev, struct dma_buf *buf,
		GFP_KERNEL);
		if (ret < 0)
		goto err;
		if (!dma_map_sg(dev, sg->sgl, sg->nents, direction)) {
		ret = -EINVAL;
		ret = dma_map_sgtable(dev, sg, direction, 0);
		if (ret < 0)
		goto err;
		}
		return sg;

		err:
		@@ -78,7 +77,7 @@ err:
		static void put_sg_table(struct device dev, struct sg_table sg,
		enum dma_data_direction direction)
		{
		dma_unmap_sg(dev, sg->sgl, sg->nents, direction);
		dma_unmap_sgtable(dev, sg, direction, 0);
		sg_free_table(sg);
		kfree(sg);
		}

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