mctp: Add base packet definitions

Simple packet header format as defined by DMTF DSP0236.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -11037,6 +11037,7 @@ M:	Jeremy Kerr <jk@codeconstruct.com.au>
 M:	Matt Johnston <matt@codeconstruct.com.au>
 L:	netdev@vger.kernel.org
 S:	Maintained
+F:	include/net/mctp.h
 F:	net/mctp/
 
 MAN-PAGES: MANUAL PAGES FOR LINUX -- Sections 2, 3, 4, 5, and 7

include/net/mctp.h

@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Management Component Transport Protocol (MCTP)
+ *
+ * Copyright (c) 2021 Code Construct
+ * Copyright (c) 2021 Google
+ */
+
+#ifndef __NET_MCTP_H
+#define __NET_MCTP_H
+
+#include <linux/bits.h>
+
+/* MCTP packet definitions */
+struct mctp_hdr {
+	u8	ver;
+	u8	dest;
+	u8	src;
+	u8	flags_seq_tag;
+};
+
+#define MCTP_VER_MIN	1
+#define MCTP_VER_MAX	1
+
+/* Definitions for flags_seq_tag field */
+#define MCTP_HDR_FLAG_SOM	BIT(7)
+#define MCTP_HDR_FLAG_EOM	BIT(6)
+#define MCTP_HDR_FLAG_TO	BIT(3)
+#define MCTP_HDR_FLAGS		GENMASK(5, 3)
+#define MCTP_HDR_SEQ_SHIFT	4
+#define MCTP_HDR_SEQ_MASK	GENMASK(1, 0)
+#define MCTP_HDR_TAG_SHIFT	0
+#define MCTP_HDR_TAG_MASK	GENMASK(2, 0)
+
+#endif /* __NET_MCTP_H */