dma-mapping: remove the DMA_ATTR_WRITE_BARRIER flag

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.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

Documentation/DMA-attributes.txt

@@ -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
 ----------------------
 

drivers/infiniband/core/umem.c

@@ -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;

include/linux/dma-mapping.h

@@ -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.