[PATCH 1/3 v3] dma: document dma_{un}map_{single|sg}_attrs() interface

akepner
2008-02-28T03:26:24Z

Document the new dma_{un}map_{single|sg}_attrs() functions.

Signed-off-by: Arthur Kepner <akepner@sgi.com>
Acked-by: Grant Grundler <grundler@parisc-linux.org>

---

DMA-API.txt | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++
DMA-attributes.txt | 29 +++++++++++++++++++++++
2 files changed, 94 insertions(+)

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index b939ebb..fdb82b0 100644
--- a/Documentation/DMA-API.txt
+++ b/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 --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index e69de29..36baea5 100644
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -0,0 +1,29 @@
+ DMA attributes
+ ==============
+
+This document describes the semantics of the DMA attributes that are
+defined in linux/dma-attrs.h.
+
+
+DMA_ATTR_SYNC_ON_WRITE
+----------------------
+
+DMA_ATTR_SYNC_ON_WRITE is used on the IA64_SGI_SN2 architecture.
+It provides a mechanism for devices to explicitly order their DMA
+writes.
+
+On IA64_SGI_SN2 machines, DMA may be reordered within the NUMA
+interconnect. Allowing reordering improves performance, but in some
+situations it may be necessary to ensure that one DMA write is
+complete before another is visible. For example, if the device does
+a DMA write to indicate that data is available in memory, DMA of the
+"completion indication" can race with DMA of data.
+
+When a memory region is mapped with the DMA_ATTR_SYNC_ON_WRITE attribute,
+a write to that region causes all in-flight DMA to be flushed to memory.
+Any pending DMA will complete and be visible in memory before the write
+to the region with the DMA_ATTR_SYNC_ON_WRITE attribute becomes visible.
+
+(For more information, see the document titled "SGI Altix Architecture
+Considerations for Linux Device Drivers" at http://techpubs.sgi.com/.)
+