Documentation/core-api/dma-attributes.rst

2 DMA attributes
5 This document describes the semantics of the DMA attributes that are
6 defined in linux/dma-mapping.h.
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15 those that do not will simply ignore the attribute and exhibit default
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25 those that do not will simply ignore the attribute and exhibit default
29 --------------------------
33 such mapping is non-trivial task and consumes very limited resources
34 (like kernel virtual address space or dma consistent address space).
44 attribute and exhibit default behavior.
47 ----------------------
49 By default dma_map_{single,page,sg} functions family transfer a given
58 depending on the dma direction). However, next calls to
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73 By default DMA-mapping subsystem is allowed to assemble the buffer
75 be mapped as contiguous chunk into device dma address space. By
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82 This is a hint to the DMA-mapping subsystem that it's probably not worth
87 - You know that the accesses to this memory won't thrash the TLB.
89   that they aren't sequential but it's unlikely you'll ping-pong
92 - You know that the penalty of TLB misses while accessing the
96 - You know that the DMA mapping is fairly transitory.  If you expect
108 ----------------
110 This tells the DMA-mapping subsystem to suppress allocation failure reports
125 -------------------
128 accesses to DMA buffers in both privileged "supervisor" and unprivileged
129 "user" modes.  This attribute is used to indicate to the DMA-mapping
131 level (and ideally inaccessible or at least read-only at the
132 lesser-privileged levels).