[PATCH 1/3] dma-mapping: introduce the DMA_ATTR_NO_WARN attribute

Mauricio Faria de Oliveira mauricfo at linux.vnet.ibm.com
Tue Aug 2 09:05:04 AEST 2016

Introduce the DMA_ATTR_NO_WARN attribute, and document it.

Signed-off-by: Mauricio Faria de Oliveira <mauricfo at linux.vnet.ibm.com>
 Documentation/DMA-attributes.txt | 17 +++++++++++++++++
 include/linux/dma-mapping.h      |  5 +++++
 2 files changed, 22 insertions(+)

diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index 2d455a5..98bf7ac 100644
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -126,3 +126,20 @@ means that we won't try quite as hard to get them.
 NOTE: At the moment DMA_ATTR_ALLOC_SINGLE_PAGES is only implemented on ARM,
 though ARM64 patches will likely be posted soon.
+This tells the DMA-mapping subsystem to suppress allocation failure reports
+(similarly to __GFP_NOWARN).
+On some architectures allocation failures are reported with error messages
+to the system logs.  Although this can help to identify and debug problems,
+drivers which handle failures (eg, retry later) have no problems with them,
+and can actually flood the system logs with error messages that aren't any
+problem at all, depending on the implementation of the retry mechanism.
+So, this provides a way for drivers to avoid those error messages on calls
+where allocation failures are not a problem, and shouldn't bother the logs.
+NOTE: At the moment DMA_ATTR_NO_WARN is only implemented on PowerPC.
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 66533e1..6efbd27 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -56,6 +56,11 @@
  * that gives better TLB efficiency.
+ * DMA_ATTR_NO_WARN: This tells the DMA-mapping subsystem to suppress
+ * allocation failure reports (similarly to __GFP_NOWARN).
+ */
+#define DMA_ATTR_NO_WARN	(1UL << 8)
  * A dma_addr_t can hold any valid DMA or bus address for the platform.

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