Ethernet provides a wide variety of layer 1 protocols and standards for
data transmission. The front-facing ports of an interface have their own
complexity and configurability.
Introduce a representation of these front-facing ports. The current code
is minimalistic and only support ports controlled by PHY devices, but
the plan is to extend that to SFP as well as raw Ethernet MACs that
don't use PHY devices.
This minimal port representation allows describing the media and number
of lanes of a port. From that information, we can derive the linkmodes
usable on the port, which can be used to limit the capabilities of an
interface.
For now, the port lanes and medium is derived from devicetree, defined
by the PHY driver, or populated with default values (as we assume that
all PHYs expose at least one port).
The typical example is 100M ethernet. 100BaseT can work using only 2
lanes on a Cat 5 cables. However, in the situation where a 10/100/1000
capable PHY is wired to its RJ45 port through 2 lanes only, we have no
way of detecting that. The "max-speed" DT property can be used, but a
more accurate representation can be used :
mdi {
port-0 {
media = "BaseT";
lanes = <2>;
};
};
