About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / DMA-attributes.txt




Custom Search

Based on kernel version 3.2. Page generated on 2012-01-05 23:28 EST.

1				DMA attributes
2				==============
3	
4	This document describes the semantics of the DMA attributes that are
5	defined in linux/dma-attrs.h.
6	
7	DMA_ATTR_WRITE_BARRIER
8	----------------------
9	
10	DMA_ATTR_WRITE_BARRIER is a (write) barrier attribute for DMA.  DMA
11	to a memory region with the DMA_ATTR_WRITE_BARRIER attribute forces
12	all pending DMA writes to complete, and thus provides a mechanism to
13	strictly order DMA from a device across all intervening busses and
14	bridges.  This barrier is not specific to a particular type of
15	interconnect, it applies to the system as a whole, and so its
16	implementation must account for the idiosyncracies of the system all
17	the way from the DMA device to memory.
18	
19	As an example of a situation where DMA_ATTR_WRITE_BARRIER would be
20	useful, suppose that a device does a DMA write to indicate that data is
21	ready and available in memory.  The DMA of the "completion indication"
22	could race with data DMA.  Mapping the memory used for completion
23	indications with DMA_ATTR_WRITE_BARRIER would prevent the race.
24	
25	DMA_ATTR_WEAK_ORDERING
26	----------------------
27	
28	DMA_ATTR_WEAK_ORDERING specifies that reads and writes to the mapping
29	may be weakly ordered, that is that reads and writes may pass each other.
30	
31	Since it is optional for platforms to implement DMA_ATTR_WEAK_ORDERING,
32	those that do not will simply ignore the attribute and exhibit default
33	behavior.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog
Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.