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dma-mapping: remove the DMA_ATTR_WRITE_BARRIER flag

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This flag is not implemented by any backend and only set by the ib_umem
module in a single instance.

Link: https://lore.kernel.org/r/20191113073214.9514-2-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
This commit is contained in:
Christoph Hellwig 2019-11-13 08:32:13 +01:00 committed by Jason Gunthorpe
parent 64c264872b
commit 7283fff8b5
3 changed files with 3 additions and 29 deletions
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18
Documentation/DMA-attributes.txt
View File

@ -5,24 +5,6 @@ DMA attributes
This document describes the semantics of the DMA attributes that are
defined in linux/dma-mapping.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 idiosyncrasies 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.
DMA_ATTR_WEAK_ORDERING
----------------------

9
drivers/infiniband/core/umem.c
View File

@ -199,7 +199,6 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr,
struct mm_struct *mm;
unsigned long npages;
int ret;
unsigned long dma_attrs = 0;
struct scatterlist *sg;
unsigned int gup_flags = FOLL_WRITE;
@ -211,9 +210,6 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr,
if (!context)
return ERR_PTR(-EIO);
if (dmasync)
dma_attrs |= DMA_ATTR_WRITE_BARRIER;
/*
* If the combination of the addr and size requested for this memory
* region causes an integer overflow, return error.
@ -294,11 +290,10 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr,
sg_mark_end(sg);
umem->nmap = ib_dma_map_sg_attrs(context->device,
umem->nmap = ib_dma_map_sg(context->device,
umem->sg_head.sgl,
umem->sg_nents,
DMA_BIDIRECTIONAL,
dma_attrs);
DMA_BIDIRECTIONAL);
if (!umem->nmap) {
ret = -ENOMEM;

5
include/linux/dma-mapping.h
View File

@ -15,11 +15,8 @@
/**
* List of possible attributes associated with a DMA mapping. The semantics
* of each attribute should be defined in Documentation/DMA-attributes.txt.
*
* DMA_ATTR_WRITE_BARRIER: DMA to a memory region with this attribute
* forces all pending DMA writes to complete.
*/
#define DMA_ATTR_WRITE_BARRIER (1UL << 0)
/*
* DMA_ATTR_WEAK_ORDERING: Specifies that reads and writes to the mapping
* may be weakly ordered, that is that reads and writes may pass each other.