In linux device tree there is configuration for sdio clock-frequency:
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_usdhc2_2>;
bus-width = <4>;
clock-frequency = <40000000>;
max-frequency = <40000000>;
status = "okay";
But in u-boot I don't find such configuration, so I wander, how is it that u-boot can manage working with sdio in a slower rate, while linux need to be configured for that rate in device tree ?