Commit 84404614 authored Apr 28, 2020 by Marek Szyprowski

drm: exynos: 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: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Acked-by : Inki Dae <inki.dae@samsung.com>

parent 10740255

drivers/gpu/drm/exynos/exynos_drm_g2d.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -395,8 +395,8 @@ static void g2d_userptr_put_dma_addr(struct g2d_data *g2d,
		return;

		out:
		dma_unmap_sg(to_dma_dev(g2d->drm_dev), g2d_userptr->sgt->sgl,
		g2d_userptr->sgt->nents, DMA_BIDIRECTIONAL);
		dma_unmap_sgtable(to_dma_dev(g2d->drm_dev), g2d_userptr->sgt,
		DMA_BIDIRECTIONAL, 0);

		pages = frame_vector_pages(g2d_userptr->vec);
		if (!IS_ERR(pages)) {
		@@ -511,10 +511,10 @@ static dma_addr_t g2d_userptr_get_dma_addr(struct g2d_data g2d,

		g2d_userptr->sgt = sgt;

		if (!dma_map_sg(to_dma_dev(g2d->drm_dev), sgt->sgl, sgt->nents,
		DMA_BIDIRECTIONAL)) {
		ret = dma_map_sgtable(to_dma_dev(g2d->drm_dev), sgt,
		DMA_BIDIRECTIONAL, 0);
		if (ret) {
		DRM_DEV_ERROR(g2d->dev, "failed to map sgt with dma region.\n");
		ret = -ENOMEM;
		goto err_sg_free_table;
		}

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