to the switch port MDIO registers. If unavailable return a negative error
code.
-- poll_link: Function invoked by DSA to query the link state of the switch
- builtin Ethernet PHYs, per port. This function is responsible for calling
- netif_carrier_{on,off} when appropriate, and can be used to poll all ports in a
- single call. Executes from workqueue context.
-
- adjust_link: Function invoked by the PHY library when a slave network device
is attached to a PHY device. This function is responsible for appropriately
configuring the switch port link parameters: speed, duplex, pause based on