entry in clock-names
  - clock-names : must contain
        "sys_ck": for clock of xHCI MAC
+       "ref_ck": for reference clock of xHCI MAC
        "wakeup_deb_p0": for USB wakeup debounce clock of port0
        "wakeup_deb_p1": for USB wakeup debounce clock of port1
 
        reg-names = "mac", "ippc";
        interrupts = <GIC_SPI 115 IRQ_TYPE_LEVEL_LOW>;
        power-domains = <&scpsys MT8173_POWER_DOMAIN_USB>;
-       clocks = <&topckgen CLK_TOP_USB30_SEL>,
+       clocks = <&topckgen CLK_TOP_USB30_SEL>, <&clk26m>,
                 <&pericfg CLK_PERI_USB0>,
                 <&pericfg CLK_PERI_USB1>;
-       clock-names = "sys_ck",
+       clock-names = "sys_ck", "ref_ck",
                      "wakeup_deb_p0",
                      "wakeup_deb_p1";
        phys = <&phy_port0 PHY_TYPE_USB3>,
        entry in clock-names
  - clock-names : must be
        "sys_ck": for clock of xHCI MAC
+       "ref_ck": for reference clock of xHCI MAC
 
 Optional properties:
  - vbus-supply : reference to the VBUS regulator;
        reg-names = "mac";
        interrupts = <GIC_SPI 115 IRQ_TYPE_LEVEL_LOW>;
        power-domains = <&scpsys MT8173_POWER_DOMAIN_USB>;
-       clocks = <&topckgen CLK_TOP_USB30_SEL>;
-       clock-names = "sys_ck";
+       clocks = <&topckgen CLK_TOP_USB30_SEL>, <&clk26m>;
+       clock-names = "sys_ck", "ref_ck";
        vusb33-supply = <&mt6397_vusb_reg>;
        usb3-lpm-capable;
 };