mirror of
https://github.com/BobTheBlinker/android_kernel_motorola_sm6375.git
synced 2026-11-08 11:45:53 -05:00
a75b0a2f68
Document the new dma_*map*_attrs() functions. [[email protected]: fix up for dma-add-dma_map_attrs-interfaces and update docs] Signed-off-by: Arthur Kepner <[email protected]> Acked-by: David S. Miller <[email protected]> Cc: Tony Luck <[email protected]> Cc: Jesse Barnes <[email protected]> Cc: Jes Sorensen <[email protected]> Cc: Randy Dunlap <[email protected]> Cc: Roland Dreier <[email protected]> Cc: James Bottomley <[email protected]> Cc: Benjamin Herrenschmidt <[email protected]> Cc: Grant Grundler <[email protected]> Cc: Michael Ellerman <[email protected]> Signed-off-by: Mark Nelson <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
24 lines
1 KiB
Text
24 lines
1 KiB
Text
DMA attributes
|
|
==============
|
|
|
|
This document describes the semantics of the DMA attributes that are
|
|
defined in linux/dma-attrs.h.
|
|
|
|
DMA_ATTR_WRITE_BARRIER
|
|
----------------------
|
|
|
|
DMA_ATTR_WRITE_BARRIER is a (write) barrier attribute for DMA. DMA
|
|
to a memory region with the DMA_ATTR_WRITE_BARRIER attribute forces
|
|
all pending DMA writes to complete, and thus provides a mechanism to
|
|
strictly order DMA from a device across all intervening busses and
|
|
bridges. This barrier is not specific to a particular type of
|
|
interconnect, it applies to the system as a whole, and so its
|
|
implementation must account for the idiosyncracies of the system all
|
|
the way from the DMA device to memory.
|
|
|
|
As an example of a situation where DMA_ATTR_WRITE_BARRIER would be
|
|
useful, suppose that a device does a DMA write to indicate that data is
|
|
ready and available in memory. The DMA of the "completion indication"
|
|
could race with data DMA. Mapping the memory used for completion
|
|
indications with DMA_ATTR_WRITE_BARRIER would prevent the race.
|
|
|