| Message ID | 20200513133245.6408-33-m.szyprowski@samsung.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v5,01/38] dma-mapping: add generic helpers for mapping sgtable objects | expand |
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@samsung.com> > --- > 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@samsung.com/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@gmail.com>
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;
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> --- 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@samsung.com/T/ --- drivers/staging/media/tegra-vde/iommu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)