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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>
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| .. | ||
| armada_510.c | ||
| armada_crtc.c | ||
| armada_crtc.h | ||
| armada_debugfs.c | ||
| armada_drm.h | ||
| armada_drv.c | ||
| armada_fb.c | ||
| armada_fb.h | ||
| armada_fbdev.c | ||
| armada_gem.c | ||
| armada_gem.h | ||
| armada_hw.h | ||
| armada_ioctlP.h | ||
| armada_overlay.c | ||
| armada_plane.c | ||
| armada_plane.h | ||
| armada_trace.c | ||
| armada_trace.h | ||
| Kconfig | ||
| Makefile | ||