diff --git a/Documentation/media/uapi/dvb/ca-set-descr.rst b/Documentation/media/uapi/dvb/ca-set-descr.rst
index 9c484317d55c170e1cdd29cb46cecd7f1c53c02b..a6c47205ffd859514c881a2b38ec69b3cec0d42b 100644
--- a/Documentation/media/uapi/dvb/ca-set-descr.rst
+++ b/Documentation/media/uapi/dvb/ca-set-descr.rst
@@ -28,22 +28,11 @@ Arguments
 ``msg``
   Pointer to struct :c:type:`ca_descr`.
 
-.. c:type:: ca_descr
-
-.. code-block:: c
-
-    struct ca_descr {
-	unsigned int index;
-	unsigned int parity;
-	unsigned char cw[8];
-    };
-
-
 Description
 -----------
 
-.. note:: This ioctl is undocumented. Documentation is welcome.
-
+CA_SET_DESCR is used for feeding descrambler CA slots with descrambling
+keys (refered as control words).
 
 Return Value
 ------------
diff --git a/include/uapi/linux/dvb/ca.h b/include/uapi/linux/dvb/ca.h
index 7ee641b4124cd17b445834b872a2a2437bc156fe..c36fdb8e27339950212c11b941919bb19badbf61 100644
--- a/include/uapi/linux/dvb/ca.h
+++ b/include/uapi/linux/dvb/ca.h
@@ -109,9 +109,16 @@ struct ca_msg {
 	unsigned char msg[256];
 };
 
+/**
+ * struct ca_descr - CA descrambler control words info
+ *
+ * @index: CA Descrambler slot
+ * @parity: control words parity, where 0 means even and 1 means odd
+ * @cw: CA Descrambler control words
+ */
 struct ca_descr {
 	unsigned int index;
-	unsigned int parity;	/* 0 == even, 1 == odd */
+	unsigned int parity;
 	unsigned char cw[8];
 };