diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
index 968d5d50751dc120b406f54fffca49b46eafa230..bdceb7411de3b2fb45e3a2f937e158f412deea5e 100644
--- a/drivers/net/usb/qmi_wwan.c
+++ b/drivers/net/usb/qmi_wwan.c
@@ -271,6 +271,11 @@ static int qmi_wwan_suspend(struct usb_interface *intf, pm_message_t message)
 	struct qmi_wwan_state *info = (void *)&dev->data;
 	int ret;
 
+	/*
+	 * Both usbnet_suspend() and subdriver->suspend() MUST return 0
+	 * in system sleep context, otherwise, the resume callback has
+	 * to recover device from previous suspend failure.
+	 */
 	ret = usbnet_suspend(intf, message);
 	if (ret < 0)
 		goto err;