Merge branches 'pm-core', 'pm-qos', 'pm-domains' and 'pm-opp'

[linux.git] / Documentation / DMA-attributes.txt

diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index 2d455a5cf6718639062e237ff859fc045d7f4911..44c6bc496eee6b140a779afa7b159c0a261326b9 100644 (file)
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -126,3 +126,30 @@ 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.
+
+DMA_ATTR_NO_WARN
+----------------
+
+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.
+
+DMA_ATTR_PRIVILEGED
+------------------------------
+
+Some advanced peripherals such as remote processors and GPUs perform
+accesses to DMA buffers in both privileged "supervisor" and unprivileged
+"user" modes.  This attribute is used to indicate to the DMA-mapping
+subsystem that the buffer is fully accessible at the elevated privilege
+level (and ideally inaccessible or at least read-only at the
+lesser-privileged levels).