[query] how to use "ranges" in device tree

[Arnd Bergmann]

On Friday 17 April 2015 11:50:16 Jisheng Zhang wrote:
> Hi all,
> 
> I got the solution, the ranges can define two or more ranges. What I need to do
> is just add ranges for 0xe0000000 - 0xf0000000 as the following:
> 
> soc {
>         ranges = <0 0xf7000000 0x1000000
>                   0xe0000000 0xe0000000 0x10000000>;  //add this line
>         ...
>         pcie: pcie at e40000 {
>                 ...
>                 reg = <0xe40000 0x10000>, <0xe0000000 0x8000000>;
>                 reg-names = "dbi", "pad", "config";
>                 ...
>         };
> }
> 
> Now, we can get the config space correctly.
> 

This will work correctly, but it is not a very clean solution, because
you define an intermediate address space that has some part of the
bus mapped to zero, and another part mapped to a high address that
matches the address the CPU sees.

A nicer (but a little more complicated) way to do this would be to use
#address-cells=<2> in the parent bus and use that to enumerate the
address ranges that get passed through:

soc {
	#address-cells=<2>;
	#size-cells=<1>;
        ranges = <0 0  0xf7000000  0x1000000>, /* 0: the normal regs */
		  <1 0  0xe0000000 0x16000000>; /* 1: reallocated registers for PCI */

	pcie at e40000 {
		#address-cells = <3>;
		#size-cells = <2>;
		reg = <0 0xe40000 0x10000>, <1 0 0x8000000>;

		/* memory space at pci address 0xf0000000, cpu address 0xf0000000, 
		   bus address 0x10000000 */
		ranges = <0x02000000 0 0xf0000000   0 0x10000000   0 0x06000000>;
	};

	...
};

The ranges property inside of the pcie node here should match whatever you program
into the inbound mapping registers of the PCIe host controller (if any).

	Arnd