The patch titled
dma: document dma_*map*_attrs() interfaces
has been added to the -mm tree. Its filename is
dma-document-dma_map_attrs-interfaces.patch
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------------------------------------------------------
Subject: dma: document dma_*map*_attrs() interfaces
From: Arthur Kepner <akepner@xxxxxxx>
Document the new dma_*map*_attrs() functions.
Signed-off-by: Arthur Kepner <akepner@xxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
Cc: Jes Sorensen <jes@xxxxxxx>
Cc: Randy Dunlap <randy.dunlap@xxxxxxxxxx>
Cc: Roland Dreier <rdreier@xxxxxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Grant Grundler <grundler@xxxxxxxxxxxxxxxx>
Cc: Michael Ellerman <michael@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/DMA-API.txt | 65 +++++++++++++++++++++++++++++
Documentation/DMA-attributes.txt | 24 ++++++++++
2 files changed, 89 insertions(+)
diff -puN Documentation/DMA-API.txt~dma-document-dma_map_attrs-interfaces Documentation/DMA-API.txt
--- a/Documentation/DMA-API.txt~dma-document-dma_map_attrs-interfaces
+++ a/Documentation/DMA-API.txt
@@ -395,6 +395,71 @@ Notes: You must do this:
See also dma_map_single().
+dma_addr_t
+dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size,
+ enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+
+void
+dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr,
+ size_t size, enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+
+int
+dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
+ int nents, enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+
+void
+dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl,
+ int nents, enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+
+The four functions above are just like the counterpart functions
+without the _attrs suffixes, except that they pass an optional
+struct dma_attrs*.
+
+struct dma_attrs encapsulates a set of "dma attributes". For the
+definition of struct dma_attrs see linux/dma-attrs.h.
+
+The interpretation of dma attributes is architecture-specific, and
+each attribute should be documented in Documentation/DMA-attributes.txt.
+
+If struct dma_attrs* is NULL, the semantics of each of these
+functions is identical to those of the corresponding function
+without the _attrs suffix. As a result dma_map_single_attrs()
+can generally replace dma_map_single(), etc.
+
+As an example of the use of the *_attrs functions, here's how
+you could pass an attribute DMA_ATTR_FOO when mapping memory
+for DMA:
+
+#include <linux/dma-attrs.h>
+/* DMA_ATTR_FOO should be defined in linux/dma-attrs.h and
+ * documented in Documentation/DMA-attributes.txt */
+...
+
+ DECLARE_DMA_ATTRS(attrs);
+ dma_set_attr(&attrs, DMA_ATTR_FOO);
+ ....
+ n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, &attr);
+ ....
+
+Architectures that care about DMA_ATTR_FOO would check for its
+presence in their implementations of the mapping and unmapping
+routines, e.g.:
+
+void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr,
+ size_t size, enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+{
+ ....
+ int foo = dma_get_attr(attrs, DMA_ATTR_FOO);
+ ....
+ if (foo)
+ /* twizzle the frobnozzle */
+ ....
+
Part II - Advanced dma_ usage
-----------------------------
diff -puN Documentation/DMA-attributes.txt~dma-document-dma_map_attrs-interfaces Documentation/DMA-attributes.txt
--- a/Documentation/DMA-attributes.txt~dma-document-dma_map_attrs-interfaces
+++ a/Documentation/DMA-attributes.txt
@@ -0,0 +1,24 @@
+ 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.
+
_
Patches currently in -mm which might be from akepner@xxxxxxx are
dma-add-dma_map_attrs-interfaces.patch
dma-document-dma_map_attrs-interfaces.patch
dma-ia64-update-ia64-machvecs-swiotlbc.patch
ib-expand-ib_umem_get-prototype.patch
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