mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-11-25 06:40:53 +07:00
a75b0a2f68
Document the new dma_*map*_attrs() functions. [markn@au1.ibm.com: fix up for dma-add-dma_map_attrs-interfaces and update docs] Signed-off-by: Arthur Kepner <akepner@sgi.com> Acked-by: David S. Miller <davem@davemloft.net> Cc: Tony Luck <tony.luck@intel.com> Cc: Jesse Barnes <jbarnes@virtuousgeek.org> Cc: Jes Sorensen <jes@sgi.com> Cc: Randy Dunlap <randy.dunlap@oracle.com> Cc: Roland Dreier <rdreier@cisco.com> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Grant Grundler <grundler@parisc-linux.org> Cc: Michael Ellerman <michael@ellerman.id.au> Signed-off-by: Mark Nelson <markn@au1.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
25 lines
1.0 KiB
Plaintext
25 lines
1.0 KiB
Plaintext
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.
|
|
|