net: mctp: Expose transport binding identifier via IFLA attribute

MCTP control protocol implementations are transport binding dependent.
Endpoint discovery is mandatory based on transport binding.
Message timing requirements are specified in each respective transport
binding specification.

However, we currently have no means to get this information from MCTP
links.

Add a IFLA_MCTP_PHYS_BINDING netlink link attribute, which represents
the transport type using the DMTF DSP0239-defined type numbers, returned
as part of RTM_GETLINK data.

We get an IFLA_MCTP_PHYS_BINDING attribute for each MCTP link, for
example:

- 0x00 (unspec) for loopback interface;
- 0x01 (SMBus/I2C) for mctpi2c%d interfaces; and
- 0x05 (serial) for mctpserial%d interfaces.

Signed-off-by: Khang Nguyen <khangng@os.amperecomputing.com>
Reviewed-by: Matt Johnston <matt@codeconstruct.com.au>
Link: https://patch.msgid.link/20241105071915.821871-1-khangng@os.amperecomputing.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/net/mctp.h b/include/net/mctp.h
index 28d59ae94ca3..1ecbff7116f6 100644
--- a/include/net/mctp.h
+++ b/include/net/mctp.h
@@ -298,4 +298,22 @@ void mctp_routes_exit(void);
 int mctp_device_init(void);
 void mctp_device_exit(void);
 
+/* MCTP IDs and Codes from DMTF specification
+ * "DSP0239 Management Component Transport Protocol (MCTP) IDs and Codes"
+ * https://www.dmtf.org/sites/default/files/standards/documents/DSP0239_1.11.1.pdf
+ */
+enum mctp_phys_binding {
+	MCTP_PHYS_BINDING_UNSPEC	= 0x00,
+	MCTP_PHYS_BINDING_SMBUS		= 0x01,
+	MCTP_PHYS_BINDING_PCIE_VDM	= 0x02,
+	MCTP_PHYS_BINDING_USB		= 0x03,
+	MCTP_PHYS_BINDING_KCS		= 0x04,
+	MCTP_PHYS_BINDING_SERIAL	= 0x05,
+	MCTP_PHYS_BINDING_I3C		= 0x06,
+	MCTP_PHYS_BINDING_MMBI		= 0x07,
+	MCTP_PHYS_BINDING_PCC		= 0x08,
+	MCTP_PHYS_BINDING_UCIE		= 0x09,
+	MCTP_PHYS_BINDING_VENDOR	= 0xFF,
+};
+
 #endif /* __NET_MCTP_H */