Discussion of low-level PHY structures and operations, starting at include/linux/phy/phy.h and seeing where it goes from there.

struct phy {
        struct device           dev;
        int                     id;
        const struct phy_ops    *ops;
        struct mutex            mutex;
        int                     init_count;
        int                     power_count;
        struct phy_attrs        attrs;
        struct regulator        *pwr;
};