diff --git a/drivers/char/watchdog/ibmasr.c b/drivers/char/watchdog/ibmasr.c
index a32c073d29bc..4f90015be7dd 100644
--- a/drivers/char/watchdog/ibmasr.c
+++ b/drivers/char/watchdog/ibmasr.c
@@ -267,7 +267,10 @@ static int asr_ioctl(struct inode *inode, struct file *file,
 			asr_toggle();
 			return 0;
 
-
+		/*
+		 * The hardware has a fixed timeout value, so WDIOC_SETTIMEOUT
+		 * is a noop and WDIOC_GETTIMEOUT always returns 256.
+		 */
 		case WDIOC_SETTIMEOUT:
 			if (get_user(heartbeat, p))
 				return -EFAULT;