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;
};

struct phy_attrs {
        u32                     bus_width;
        enum phy_mode           mode;
};

enum phy_mode {
        PHY_MODE_INVALID,
        PHY_MODE_USB_HOST,
        PHY_MODE_USB_HOST_LS,
        PHY_MODE_USB_HOST_FS,
        PHY_MODE_USB_HOST_HS,
        PHY_MODE_USB_HOST_SS,
        PHY_MODE_USB_DEVICE,
        PHY_MODE_USB_DEVICE_LS,
        PHY_MODE_USB_DEVICE_FS,
        PHY_MODE_USB_DEVICE_HS,
        PHY_MODE_USB_DEVICE_SS,
        PHY_MODE_USB_OTG,
        PHY_MODE_SGMII,
        PHY_MODE_2500SGMII,
        PHY_MODE_QSGMII,
        PHY_MODE_10GKR,
        PHY_MODE_UFS_HS_A,
        PHY_MODE_UFS_HS_B,
        PHY_MODE_PCIE,
};