13.05.2020 16:32, Marek Szyprowski пишет:
> 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@xxxxxxxxxxx>
> ---
> For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents
> vs. orig_nents misuse' thread:
> https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@xxxxxxxxxxx/T/
> ---
> drivers/staging/media/tegra-vde/iommu.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/media/tegra-vde/iommu.c b/drivers/staging/media/tegra-vde/iommu.c
> index 6af863d..adf8dc7 100644
> --- a/drivers/staging/media/tegra-vde/iommu.c
> +++ b/drivers/staging/media/tegra-vde/iommu.c
> @@ -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;
>
Reviewed-by: Dmitry Osipenko <digetx@xxxxxxxxx>
