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staging: tegra-vde: fix common struct sg_table related issues

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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: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20200904131711.12950-27-m.szyprowski@samsung.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Marek Szyprowski 2020-09-04 15:17:07 +02:00 committed by Greg Kroah-Hartman
parent 19bad6999d
commit 76f50ad9b1
1 changed files with 2 additions and 2 deletions
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4
drivers/staging/media/tegra-vde/iommu.c
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@ -36,8 +36,8 @@ int tegra_vde_iommu_map(struct tegra_vde *vde,
addr = iova_dma_addr(&vde->iova, iova);
size = iommu_map_sg(vde->domain, addr, sgt->sgl, sgt->nents,
IOMMU_READ | IOMMU_WRITE);
size = iommu_map_sgtable(vde->domain, addr, sgt,
IOMMU_READ | IOMMU_WRITE);
if (!size) {
__free_iova(&vde->iova, iova);
return -ENXIO;