Re: [PATCH] net: dsa: read mac address from DT for slave device

[Florian Fainelli <f.fainelli@gmail.com>]

On 2/25/19 5:28 AM, xiaofeis@codeaurora.org wrote:
> Hi Florian
> 
> We have two slave DSA interfaces, wan0 and lan0, one is for wan port,
> and the other is for lan port. Customer has it's mac address pool, they
> want
> to assign the mac address from the pool on wan0, lan0, and other
> interfaces like
> wifi, bt. Coreboot/uboot will populate it to the DTS node, so the driver
> can
> get it from it's node. For DSA slave interface, it already has it's own
> DTS node, it's
> easy to just add one porperty "local-mac-address" there for the usage in
> DSA driver.
> 
> If not use DSA framework, normally we will use eth0.x and eth0.y for wan
> and lan.
> On this case, customer usually also assign the MAC address on these
> logical interface
> from it's pool.

OK, but this is not necessary per my previous explanation: the CPU <=>
WAN pipe is a separate broadcast domain (otherwise it is a security hole
since you exposing LAN machines to the outside world), and so there is
no need for a separate MAC address. It might be convenient to have one,
especially for the provider, if they run a management software (e.g.:
TR69), but it is not required per-se.

Let me ask a secondary question here, how many Ethernet MACs connect to
the switch in this configuration? Is there one that is supposed to be
assigned all LAN traffic and one that is supposed to be assigned all WAN
traffic? If so, then what you are doing makes even less

> 
> On 2019-02-22 23:43, Florian Fainelli wrote:
>> On 2/22/19 4:58 AM, Vinod Koul wrote:
>>> From: Xiaofei Shen <xiaofeis@codeaurora.org>
>>>
>>> Before creating a slave netdevice, get the mac address from DTS and
>>> apply in case it is valid.
>>
>> Can you explain your use case in details?
>>
>> Assigning a MAC address to a network device that represents a switch
>> port does not quite make sense in general. The switch port is really
>> representing one end of a pipe, so one side you have stations and on the
>> other side, you have the CPU/management Ethernet MAC controller's MAC
>> address which constitutes a station as well. The DSA slave network
>> devices are just software constructs meant to steer traffic towards
>> specific ports of the switch, but they are all from the perpsective of
>> traffic reaching the CPU Port in the first place, therefore traffic that
>> is generally a known unicast Ethernet frame with the CPU's MAC address
>> as MAC DA (and of course all types of unknown MC, management traffic
>> etc.)
>>
>> By default, DSA switch need to come up in a configuration where all
>> ports (except CPU/management) must be strictly separate from every other
>> port such that we can achieve what a standalone Ethernet NIC would do.
>> This works because all ports are isolated from one another, so there is
>> no cross talk and so having the same MAC address (the one from the CPU)
>> on the DSA slave network devices just works, each port is a separate
>> broadcast domain.
>>
>> Once you start bridging one or ore ports, the bridge root port will have
>> a MAC address, most likely the one the CPU/management Ethernet MAC, but
>> similarly, this is not an issue and that's exactly how a software bridge
>> would work as well.
>>
>>>
>>> Signed-off-by: Xiaofei Shen <xiaofeis@codeaurora.org>
>>> Signed-off-by: Vinod Koul <vkoul@kernel.org>
>>> ---
>>>  include/net/dsa.h | 1 +
>>>  net/dsa/dsa2.c    | 1 +
>>>  net/dsa/slave.c   | 5 ++++-
>>>  3 files changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/include/net/dsa.h b/include/net/dsa.h
>>> index b3eefe8e18fd..aa24ce756679 100644
>>> --- a/include/net/dsa.h
>>> +++ b/include/net/dsa.h
>>> @@ -198,6 +198,7 @@ struct dsa_port {
>>>      unsigned int        index;
>>>      const char        *name;
>>>      const struct dsa_port    *cpu_dp;
>>> +    const char        *mac;
>>>      struct device_node    *dn;
>>>      unsigned int        ageing_time;
>>>      u8            stp_state;
>>> diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
>>> index a1917025e155..afb7d9fa42f6 100644
>>> --- a/net/dsa/dsa2.c
>>> +++ b/net/dsa/dsa2.c
>>> @@ -261,6 +261,7 @@ static int dsa_port_setup(struct dsa_port *dp)
>>>      int err = 0;
>>>
>>>      memset(&dp->devlink_port, 0, sizeof(dp->devlink_port));
>>> +    dp->mac = of_get_mac_address(dp->dn);
>>>
>>>      if (dp->type != DSA_PORT_TYPE_UNUSED)
>>>          err = devlink_port_register(ds->devlink, &dp->devlink_port,
>>> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
>>> index a3fcc1d01615..8e64c4e947c6 100644
>>> --- a/net/dsa/slave.c
>>> +++ b/net/dsa/slave.c
>>> @@ -1308,7 +1308,10 @@ int dsa_slave_create(struct dsa_port *port)
>>>      slave_dev->features = master->vlan_features | NETIF_F_HW_TC;
>>>      slave_dev->hw_features |= NETIF_F_HW_TC;
>>>      slave_dev->ethtool_ops = &dsa_slave_ethtool_ops;
>>> -    eth_hw_addr_inherit(slave_dev, master);
>>> +    if (port->mac && is_valid_ether_addr(port->mac))
>>> +        ether_addr_copy(slave_dev->dev_addr, port->mac);
>>> +    else
>>> +        eth_hw_addr_inherit(slave_dev, master);
>>>      slave_dev->priv_flags |= IFF_NO_QUEUE;
>>>      slave_dev->netdev_ops = &dsa_slave_netdev_ops;
>>>      slave_dev->switchdev_ops = &dsa_slave_switchdev_ops;
>>>


-- 
Florian