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Marek Szyprowski authored
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. This driver creatively uses sg_table->orig_nents to store the size of the allocated scatterlist and ignores the number of the entries returned by dma_map_sg function. The sg_table->orig_nents is (mis)used to properly free the (over)allocated scatterlist. This patch only introduces the common DMA-mapping wrappers operating directly on the struct sg_table objects to the dmabuf related functions, so the other drivers, which might share buffers with i915 could rely on the properly set nents and orig_nents values. Signed-off-by:
Marek Szyprowski <m.szyprowski@samsung.com> Reviewed-by:
Robin Murphy <robin.murphy@arm.com> Reviewed-by:
Michael J. Ruhl <michael.j.ruhl@intel.com>
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