Set reference clock for onboard hub in DT

[Frieder Schrempf <frieder.schrempf@xxxxxxxxx>]

Hi,

I have a question concerning the setup for a board with an onboard USB 
hub. The SoC (i.MX6S) is expected to provide a 12 MHz clock on one of 
the clock output pins as a reference for the USB hub.

Now I was looking for a way to configure this in the DT, which works 
fine up to the point, that there doesn't seem to be a way to set a 
reference clock for a generic USB device.

Would it make sense to implement the enabling/disabling of the clock in 
the generic USB device driver?
It doesn't seem right to write a separate driver for the hub only to 
turn the clock on and off.

My intended DT setup would look something like this:

&usbh1 {
	vbus-supply = <&reg_usb_h1_vbus>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_usbh1>;
	dr_mode = "host";
	status = "okay";
	#address-cells = <1>;
	#size-cells = <0>;

	hub@1 {
		compatible = "usb4b4,6570";
		reg = <1>;
		clocks = <&clks IMX6QDL_CLK_CKO>;
		assigned-clocks = <&clks IMX6QDL_CLK_CKO>,
				  <&clks IMX6QDL_CLK_CKO2_SEL>,
				  <&clks IMX6QDL_CLK_CKO2>;
		assigned-clock-parents = <&clks IMX6QDL_CLK_CKO2>,
					 <&clks IMX6QDL_CLK_OSC>,
					 <&clks IMX6QDL_CLK_CKO2_PODF>;
		assigned-clock-rates = <0 0 12000000>;
	}
};

Thanks,
Frieder