Query: PCIe range entry at pcie at 0 in dts files

[Kushwaha Prabhakar-B32579]

Hi all,

 I have query about usage of range field at pcie at 0 under PCIe controller. Please find snap shot from mpc8536_36.dts..

	pci3: pcie at fffe0b000 {
		compatible = "fsl,mpc8548-pcie";
		device_type = "pci";
		#interrupt-cells = <1>;
		#size-cells = <2>;
		#address-cells = <3>;
		reg = <0xf 0xffe0b000 0 0x1000>;
		bus-range = <0 0xff>;
		ranges = <0x02000000 0 0xe0000000 0xc 0x20000000 0 0x20000000
			  0x01000000 0 0x00000000 0xf 0xffc30000 0 0x00010000>;
		clock-frequency = <33333333>;
		interrupt-parent = <&mpic>;
		interrupts = <27 0x2>;
		interrupt-map-mask = <0xf800 0 0 7>;
		interrupt-map = <
			/* IDSEL 0x0 */
			0000 0 0 1 &mpic 8 1
			0000 0 0 2 &mpic 9 1
			0000 0 0 3 &mpic 10 1
			0000 0 0 4 &mpic 11 1
			>;

		pcie at 0 {
			reg = <0 0 0 0 0>;
			#size-cells = <2>;
			#address-cells = <3>;
			device_type = "pci";
			ranges = <0x02000000 0 0xe0000000 --> child/port start address
				  0x02000000 0 0xe0000000 --> Parent bus address
				  0 0x20000000

				  0x01000000 0 0x00000000
				  0x01000000 0 0x00000000
				  0 0x00100000>;
		};
	};

Question:
A) is ranges filed of pcie at 0 really required?
	 I just went through the code and found scan_OF_for_pci_dev() called from pci_busdev_to_OF_node() touches pcie at 0 node. But, It does not even uses range filed. 

	static struct device_node *scan_OF_for_pci_dev(struct device_node *parent,unsigned int devfn) {
		 ---
       	---
		for_each_child_of_node(parent, np) {
			reg = of_get_property(np, "reg", &psize); 
      
		  ---
		  ---
            	    if (!strcmp(np->name, "multifunc-device")) { 
	      
	}

   I also checked "Power_ePAPR_APPROVED_v1.0.pdf". It never say range filed required for child bus.

B) if range field of pcie at 0 required. why does child/port start address same as Parent bus address?  Range property provides mapping of port address to parent address space.
So the value should be 0x00000000. Means port's address starting from 0x00000000 to size 0x20000000 is mapped parent's 0xe0000000.

			ranges = <0x02000000 0 0x00000000  --> Child/port's start address
				  0x02000000 0 0xe0000000    --> Parent bus address
				  0 0x20000000

				  0x01000000 0 0x00000000
				  0x01000000 0 0x00000000
				  0 0x00100000>;


--Prabhakar