X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;ds=sidebyside;f=Documentation%2FDMA-API.txt;h=11caa2d64c013b405bd56f3a44382a656e62da47;hb=9bf4aaab3e101692164d49b7ca357651eb691cb6;hp=2c1bd6a83fafc6ba92eb0077af83f4e9dac3b1e7;hpb=db216c3d5e4c040e557a50f8f5d35d5c415e8c1c;p=linux-2.6.git

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index 2c1bd6a83..11caa2d64 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -162,6 +162,20 @@ parameters if it is.
 
 Returns: 1 if successful and 0 if not
 
+u64
+dma_get_required_mask(struct device *dev)
+
+After setting the mask with dma_set_mask(), this API returns the
+actual mask (within that already set) that the platform actually
+requires to operate efficiently.  Usually this means the returned mask
+is the minimum required to cover all of memory.  Examining the
+required mask gives drivers with variable descriptor sizes the
+opportunity to use smaller descriptors as necessary.
+
+Requesting the required mask does not alter the current mask.  If you
+wish to take advantage of it, you should issue another dma_set_mask()
+call to lower the mask again.
+
 
 Part Id - Streaming DMA mappings
 --------------------------------