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author | Marek Szyprowski <m.szyprowski@samsung.com> | 2020-04-30 14:57:22 +0300 |
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committer | Marek Szyprowski <m.szyprowski@samsung.com> | 2020-09-10 09:19:46 +0300 |
commit | be0704beb229431f206fee3ddd65fa2c5eebdce3 (patch) | |
tree | c3a4fcb2e39e3637d5bc5f1a61fb3415475a7c0e /arch/alpha | |
parent | 62296b395a512930686666089ad285b1f78fd2f0 (diff) | |
download | linux-be0704beb229431f206fee3ddd65fa2c5eebdce3.tar.xz |
samples: vfio-mdev/mbochs: 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.
While touching this code, also add missing call to dma_unmap_sgtable.
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Diffstat (limited to 'arch/alpha')
0 files changed, 0 insertions, 0 deletions