VServer 1.9.2 (patch-2.6.8.1-vs1.9.2.diff)

[linux-2.6.git] / Documentation / DMA-API.txt

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index 2c1bd6a..11caa2d 100644 (file)
--- 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
 --------------------------------