linux/Documentation/devicetree/bindings/net/fixed-link.txt

Fixed link Device Tree binding
------------------------------

Some Ethernet MACs have a "fixed link", and are not connected to a
normal MDIO-managed PHY device. For those situations, a Device Tree
binding allows to describe a "fixed link".

Such a fixed link situation is described by creating a 'fixed-link'
sub-node of the Ethernet MAC device node, with the following
properties:

* 'speed' (integer, mandatory), to indicate the link speed. Accepted
  values are 10, 100 and 1000
* 'full-duplex' (boolean, optional), to indicate that full duplex is
  used. When absent, half duplex is assumed.
* 'pause' (boolean, optional), to indicate that pause should be
  enabled.
* 'asym-pause' (boolean, optional), to indicate that asym_pause should
  be enabled.
* 'link-gpios' ('gpio-list', optional), to indicate if a gpio can be read
  to determine if the link is up.

Old, deprecated 'fixed-link' binding:

* A 'fixed-link' property in the Ethernet MAC node, with 5 cells, of the
  form <a b c d e> with the following accepted values:
  - a: emulated PHY ID, choose any but but unique to the all specified
    fixed-links, from 0 to 31
  - b: duplex configuration: 0 for half duplex, 1 for full duplex
  - c: link speed in Mbits/sec, accepted values are: 10, 100 and 1000
  - d: pause configuration: 0 for no pause, 1 for pause
  - e: asymmetric pause configuration: 0 for no asymmetric pause, 1 for
    asymmetric pause

Examples:

ethernet@0 {
	...
	fixed-link {
	      speed = <1000>;
	      full-duplex;
	};
	...
};

ethernet@1 {
	...
	fixed-link {
	      speed = <1000>;
	      pause;
	      link-gpios = <&gpio0 12 GPIO_ACTIVE_HIGH>;
	};
	...
};