diff --git a/Documentation/core-api/dma-api-howto.rst b/Documentation/core-api/dma-api-howto.rst
index e8a55f9d61db..0bf31b6c4383 100644
--- a/Documentation/core-api/dma-api-howto.rst
+++ b/Documentation/core-api/dma-api-howto.rst
@@ -203,13 +203,33 @@ setting the DMA mask fails.  In this manner, if a user of your driver reports
 that performance is bad or that the device is not even detected, you can ask
 them for the kernel messages to find out exactly why.
 
-The standard 64-bit addressing device would do something like this::
+The 24-bit addressing device would do something like this::
 
-	if (dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64))) {
+	if (dma_set_mask_and_coherent(dev, DMA_BIT_MASK(24))) {
 		dev_warn(dev, "mydev: No suitable DMA available\n");
 		goto ignore_this_device;
 	}
 
+The standard 64-bit addressing device would do something like this::
+
+	dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64))
+
+dma_set_mask_and_coherent() never return fail when DMA_BIT_MASK(64). Typical
+error code like::
+
+	/* Wrong code */
+	if (dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64)))
+		dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32))
+
+dma_set_mask_and_coherent() will never return failure when bigger than 32.
+So typical code like::
+
+	/* Recommended code */
+	if (support_64bit)
+		dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
+	else
+		dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
+
 If the device only supports 32-bit addressing for descriptors in the
 coherent allocations, but supports full 64-bits for streaming mappings
 it would look like this::