diff --git a/kernel/dma.c b/kernel/dma.c
index aef0a45..2020644 100644
--- a/kernel/dma.c
+++ b/kernel/dma.c
@@ -62,6 +62,11 @@
 };
 
 
+/**
+ * request_dma - request and reserve a system DMA channel
+ * @dmanr: DMA channel number
+ * @device_id: reserving device ID string, used in /proc/dma
+ */
 int request_dma(unsigned int dmanr, const char * device_id)
 {
 	if (dmanr >= MAX_DMA_CHANNELS)
@@ -76,7 +81,10 @@
 	return 0;
 } /* request_dma */
 
-
+/**
+ * free_dma - free a reserved system DMA channel
+ * @dmanr: DMA channel number
+ */
 void free_dma(unsigned int dmanr)
 {
 	if (dmanr >= MAX_DMA_CHANNELS) {