AM6442: OSPI clock to flash device cycles from 133MHz to 166MHz

Hi experts,

I uses a custom board that is similar to AM64x evm board, the difference is that I uses a bigger flash device to connect to AM64x via OSPI.

When the board runs, the ospi_clock cycles from 133MHz to 166MHz then down to 133MHz and go on.

My config is: 

&ospi0 {
	pinctrl-names = "default";
	pinctrl-0 = <&ospi0_pins_default>;

	flash@0{
		compatible = "jedec,spi-nor";
		reg = <0x0>;
		spi-tx-bus-width = <8>;
		spi-rx-bus-width = <8>;
		spi-max-frequency = <25000000>;
		cdns,tshsl-ns = <60>;
		cdns,tsd2d-ns = <60>;
		cdns,tchsh-ns = <60>;
		cdns,tslch-ns = <60>;
		cdns,read-delay = <4>;
		cdns,phy-mode;
		#address-cells = <1>;
		#size-cells = <1>;
	};
};


My questions are:
1. Does the ospi clock change because I enable phy-mode(cdns,phy-mode;) for tuning? 
(When I tried to disable phy-mode the board can not boot anymore)

2. Is there any way to fix the ospi_clk?

Thank you