diff --git a/[refs] b/[refs]
index f0af8bfecd40..e1fa758317a5 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 3b9c6c11f519718d618f5d7c9508daf78b207f6f
+refs/heads/master: c31e74c4c34fa863393c28b95409aee934b4f8e1
diff --git a/trunk/Documentation/DMA-API-HOWTO.txt b/trunk/Documentation/DMA-API-HOWTO.txt
index 98ce51796f71..3c4e07123e59 100644
--- a/trunk/Documentation/DMA-API-HOWTO.txt
+++ b/trunk/Documentation/DMA-API-HOWTO.txt
@@ -753,6 +753,16 @@ to "Closing".
    alignment constraints (e.g. the alignment constraints about 64-bit
    objects).
 
+3) Supporting multiple types of IOMMUs
+
+   If your architecture needs to support multiple types of IOMMUs, you
+   can use include/linux/asm-generic/dma-mapping-common.h. It's a
+   library to support the DMA API with multiple types of IOMMUs. Lots
+   of architectures (x86, powerpc, sh, alpha, ia64, microblaze and
+   sparc) use it. Choose one to see how it can be used. If you need to
+   support multiple types of IOMMUs in a single system, the example of
+   x86 or powerpc helps.
+
 			   Closing
 
 This document, and the API itself, would not be in its current