diff --git a/include/net/nfc/hci.h b/include/net/nfc/hci.h
index ab672b537dd4618dc25c31d1e10f400c96284fd2..020a814bc8ed7145f7b7491c6c21ba07b01e9c36 100644
--- a/include/net/nfc/hci.h
+++ b/include/net/nfc/hci.h
@@ -83,6 +83,10 @@ struct nfc_hci_pipe {
 };
 
 #define NFC_HCI_MAX_CUSTOM_GATES	50
+/*
+ * According to specification 102 622 chapter 4.4 Pipes,
+ * the pipe identifier is 7 bits long.
+ */
 #define NFC_HCI_MAX_PIPES		127
 struct nfc_hci_init_data {
 	u8 gate_count;