How to get related device pointer via DT?

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Hi,

I would like to get a related device pointer on usb EHCI drivers (or USB framework)
because related device (e.g. OHCI or UHCI, called "companion controllers") has to
finish resuming. I discussed this topic with Alan:
http://marc.info/?t=148653514200001&r=1&w=2

In PCI bus, USB framework already has such a feature in drivers/usb/core/hcd-pci.c.
However, in platform devices, we don't have it for now. So, I would like to add it.

Then, I have 2 ideas to get the related device pointer:

A) We add a new property "companion" as usb-generic.txt and EHCI node(s) have
   such a property to bind a companion controller.
B) We assume EHCI controller binds a companion controller if some resources
   (irq or clock) are the same and it has a compatible strings as "generic-[uo]hci"
   for instance.

My environment is R-Car H3, and it has 3 EHCI and 3 OHCI controllers.
For example (I only wrote channel 0 of EHCI and OHCI):
		ehci0: usb@ee080100 {
			compatible = "generic-ehci";
			reg = <0 0xee080100 0 0x100>;
			interrupts = <GIC_SPI 108 IRQ_TYPE_LEVEL_HIGH>;
			clocks = <&cpg CPG_MOD 703>;
			phys = <&usb2_phy0>;
			phy-names = "usb";
			power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
			status = "disabled";
		};

		ohci0: usb@ee080000 {
			compatible = "generic-ohci";
			reg = <0 0xee080000 0 0x100>;
			interrupts = <GIC_SPI 108 IRQ_TYPE_LEVEL_HIGH>;
			clocks = <&cpg CPG_MOD 703>;
			phys = <&usb2_phy0>;
			phy-names = "usb";
			power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
			status = "disabled";
		};

If my idea A), ehci0 will have companion = <&ohci>;
If my idea B), no need to add any property.

What do you think?
Anyway, I will start to study DT programming :)

Best regards,
Yoshihiro Shimoda





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