mctp i3c: MCTP I3C driver

Provides MCTP network transport over an I3C bus, as specified in
DMTF DSP0233.

Each I3C bus (with "mctp-controller" devicetree property) gets an
"mctpi3cX" net device created. I3C devices are reachable as remote
endpoints through that net device. Link layer addressing uses the
I3C PID as a fixed hardware address for neighbour table entries.

The driver matches I3C devices that have the MIPI assigned DCR 0xCC for
MCTP.

Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

mctp i2c: MCTP I2C binding driver

Provides MCTP network transport over an I2C bus, as specified in
DMTF DSP0237. All messages between nodes are sent as SMBus Block Writes.

Each I2C bus to be used for MCTP is flagged in devicetree by a
'mctp-controller' property on the bus node. Each flagged bus gets a
mctpi2cX net device created based on the bus number. A
'mctp-i2c-controller' I2C client needs to be added under the adapter. In
an I2C mux situation the mctp-i2c-controller node must be attached only
to the root I2C bus. The I2C client will handle incoming I2C slave block
write data for subordinate busses as well as its own bus.

In configurations without devicetree a driver instance can be attached
to a bus using the I2C slave new_device mechanism.

The MCTP core will hold/release the MCTP I2C device while responses
are pending (a 6 second timeout or once a socket is closed, response
received etc). While held the MCTP I2C driver will lock the I2C bus so
that the correct I2C mux remains selected while responses are received.

(Ideally we would just lock the mux to keep the current bus selected for
the response rather than a full I2C bus lock, but that isn't exposed in
the I2C mux API)

Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Reviewed-by: Wolfram Sang <wsa@kernel.org> # I2C transport parts
Signed-off-by: David S. Miller <davem@davemloft.net>

mctp: Add MCTP-over-serial transport binding

This change adds a MCTP Serial transport binding, as defined by DMTF
specificiation DSP0253 - "MCTP Serial Transport Binding". This is
implemented as a new serial line discipline, and can be attached to
arbitrary tty devices.

From the Kconfig description:

This driver provides an MCTP-over-serial interface, through a
serial line-discipline, as defined by DMTF specification "DSP0253 -
MCTP Serial Transport Binding". By attaching the ldisc to a serial
device, we get a new net device to transport MCTP packets.

This allows communication with external MCTP endpoints which use
serial as their transport. It can also be used as an easy way to
provide MCTP connectivity between virtual machines, by forwarding
data between simple virtual serial devices.

Say y here if you need to connect to MCTP endpoints over serial. To
compile as a module, use m; the module will be called mctp-serial.

Once the N_MCTP line discipline is set [using ioctl(TCIOSETD)], we get a
new netdev suitable for MCTP communication.

The 'mctp' utility[1] provides a simple wrapper for this ioctl, using
'link serial <device>':

# mctp link serial /dev/ttyS0 &
# mctp link
dev lo index 1 address 0x00:00:00:00:00:00 net 1 mtu 65536 up
dev mctpserial0 index 5 address 0x(no-addr) net 1 mtu 68 down

[1]: https://github.com/CodeConstruct/mctp

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

Revert "Merge branch 'mctp-i2c-driver'"

This reverts commit 71812af7234f30362b43ccff33f93890ae4c0655, reversing
changes made to cc0be1ad686fb29a4d127948486f40b17fb34b50.

Wolfram Sang says:

Please revert. Besides the driver in net, it modifies the I2C core
code. This has not been acked by the I2C maintainer (in this case me).
So, please don't pull this in via the net tree. The question raised here
(extending SMBus calls to 255 byte) is complicated because we need ABI
backwards compatibility.

Link: https://lore.kernel.org/all/YZJ9H4eM%2FM7OXVN0@shikoro/
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

mctp i2c: MCTP I2C binding driver

Provides MCTP network transport over an I2C bus, as specified in
DMTF DSP0237. All messages between nodes are sent as SMBus Block Writes.

Each I2C bus to be used for MCTP is flagged in devicetree by a
'mctp-controller' property on the bus node. Each flagged bus gets a
mctpi2cX net device created based on the bus number. A
'mctp-i2c-controller' I2C client needs to be added under the adapter. In
an I2C mux situation the mctp-i2c-controller node must be attached only
to the root I2C bus. The I2C client will handle incoming I2C slave block
write data for subordinate busses as well as its own bus.

In configurations without devicetree a driver instance can be attached
to a bus using the I2C slave new_device mechanism.

The MCTP core will hold/release the MCTP I2C device while responses
are pending (a 6 second timeout or once a socket is closed, response
received etc). While held the MCTP I2C driver will lock the I2C bus so
that the correct I2C mux remains selected while responses are received.

(Ideally we would just lock the mux to keep the current bus selected for
the response rather than a full I2C bus lock, but that isn't exposed in
the I2C mux API)

This driver requires I2C adapters that allow 255 byte transfers
(SMBus 3.0) as the specification requires a minimum MTU of 68 bytes.

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

mctp: Add initial driver infrastructure

Add an empty drivers/net/mctp/, for future interface drivers.

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