netdev - [PATCH net-next v2 1/2] usb: Add base USB MCTP definitions

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Message-Id: <20250212-dev-mctp-usb-v2-1-76e67025d764@codeconstruct.com.au>
Date: Wed, 12 Feb 2025 10:46:50 +0800
From: Jeremy Kerr <jk@...econstruct.com.au>
To: Matt Johnston <matt@...econstruct.com.au>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-usb@...r.kernel.org, 
 Santosh Puranik <spuranik@...dia.com>
Subject: [PATCH net-next v2 1/2] usb: Add base USB MCTP definitions

Upcoming changes will add a USB host (and later gadget) driver for the
MCTP-over-USB protocol. Add a header that provides common definitions
for protocol support: the packet header format and a few framing
definitions. Add a define for the MCTP class code, as per
https://usb.org/defined-class-codes.

Signed-off-by: Jeremy Kerr <jk@...econstruct.com.au>

---
v2:
 - add reference & URL to DSP0283
 - update copyright year
---
 MAINTAINERS                  |  1 +
 include/linux/usb/mctp-usb.h | 30 ++++++++++++++++++++++++++++++
 include/uapi/linux/usb/ch9.h |  1 +
 3 files changed, 32 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 67665d9dd536873e94afffc00393c2fe2e8c2797..e7b326dba9a9e6f50c3beeb172d93641841f6242 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13903,6 +13903,7 @@ L:	netdev@...r.kernel.org
 S:	Maintained
 F:	Documentation/networking/mctp.rst
 F:	drivers/net/mctp/
+F:	include/linux/usb/mctp-usb.h
 F:	include/net/mctp.h
 F:	include/net/mctpdevice.h
 F:	include/net/netns/mctp.h
diff --git a/include/linux/usb/mctp-usb.h b/include/linux/usb/mctp-usb.h
new file mode 100644
index 0000000000000000000000000000000000000000..b19392aa29310eda504f65bd098c849bd02dc0a1
--- /dev/null
+++ b/include/linux/usb/mctp-usb.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * mctp-usb.h - MCTP USB transport binding: common definitions,
+ * based on DMTF0283 specification:
+ * https://www.dmtf.org/sites/default/files/standards/documents/DSP0283_1.0.1.pdf
+ *
+ * These are protocol-level definitions, that may be shared between host
+ * and gadget drivers.
+ *
+ * Copyright (C) 2024-2025 Code Construct Pty Ltd
+ */
+
+#ifndef __LINUX_USB_MCTP_USB_H
+#define __LINUX_USB_MCTP_USB_H
+
+#include <linux/types.h>
+
+struct mctp_usb_hdr {
+	__be16	id;
+	__u8	rsvd;
+	__u8	len;
+} __packed;
+
+#define MCTP_USB_XFER_SIZE	512
+#define MCTP_USB_BTU		68
+#define MCTP_USB_MTU_MIN	MCTP_USB_BTU
+#define MCTP_USB_MTU_MAX	(U8_MAX - sizeof(struct mctp_usb_hdr))
+#define MCTP_USB_DMTF_ID	0x1ab4
+
+#endif /*  __LINUX_USB_MCTP_USB_H */
diff --git a/include/uapi/linux/usb/ch9.h b/include/uapi/linux/usb/ch9.h
index 91f0f7e214a5a57c8bee3f44c4dbf7b175843d8c..052290652046591fba46f1f0cb5cf77fd965f555 100644
--- a/include/uapi/linux/usb/ch9.h
+++ b/include/uapi/linux/usb/ch9.h
@@ -330,6 +330,7 @@ struct usb_device_descriptor {
 #define USB_CLASS_AUDIO_VIDEO		0x10
 #define USB_CLASS_BILLBOARD		0x11
 #define USB_CLASS_USB_TYPE_C_BRIDGE	0x12
+#define USB_CLASS_MCTP			0x14
 #define USB_CLASS_MISC			0xef
 #define USB_CLASS_APP_SPEC		0xfe
 #define USB_SUBCLASS_DFU			0x01

-- 
2.39.5