diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
index 9a2a39df1056..c532939c1c3f 100644
--- a/drivers/s390/cio/vfio_ccw_cp.c
+++ b/drivers/s390/cio/vfio_ccw_cp.c
@@ -23,9 +23,13 @@
 #define CCWCHAIN_LEN_MAX	256
 
 struct pfn_array {
+	/* Starting guest physical I/O address. */
 	unsigned long		pa_iova;
+	/* Array that stores PFNs of the pages need to pin. */
 	unsigned long		*pa_iova_pfn;
+	/* Array that receives PFNs of the pages pinned. */
 	unsigned long		*pa_pfn;
+	/* Number of pages to pin/pinned from @pa_iova. */
 	int			pa_nr;
 };
 
@@ -53,14 +57,8 @@ struct ccwchain {
  * Attempt to pin user pages in memory.
  *
  * Usage of pfn_array:
- * @pa->pa_iova     starting guest physical I/O address. Assigned by caller.
- * @pa->pa_iova_pfn array that stores PFNs of the pages need to pin. Allocated
- *                  by caller.
- * @pa->pa_pfn      array that receives PFNs of the pages pinned. Allocated by
- *                  caller.
- * @pa->pa_nr       number of pages from @pa->pa_iova to pin. Assigned by
- *                  caller.
- *                  number of pages pinned. Assigned by callee.
+ * Any field in this structure should be initialized by caller.
+ * We expect @pa->pa_nr > 0, and its value will be assigned by callee.
  *
  * Returns:
  *   Number of pages pinned on success.