设备树 ranges 属性 更全讲解

这篇文章讲得很好，但是缺少一些知识点 

https://www.cnblogs.com/pengdonglin137/p/7401049.html

比如这种:

    smb: smb@4000000 {
        compatible = "simple-bus";

        #address-cells = <2>;
        #size-cells = <1>;
        ranges = <0 0 0x40000000 0x04000000>,
             <1 0 0x44000000 0x04000000>,
             <2 0 0x48000000 0x04000000>,
             <3 0 0x4c000000 0x04000000>,
             <7 0 0x10000000 0x00020000>;

    smb@4000000 {
        motherboard {
            model = "V2M-P1";
            arm,hbi = <0x190>;
            arm,vexpress,site = <0>;
            compatible = "arm,vexpress,v2m-p1", "simple-bus";
            #address-cells = <2>; /* SMB chipselect number and offset */
            #size-cells = <1>;
            #interrupt-cells = <1>;
            ranges;

            flash@0,00000000 {
                compatible = "arm,vexpress-flash", "cfi-flash";
                reg = <0 0x00000000 0x04000000>,
                      <1 0x00000000 0x04000000>;
                bank-width = <4>;
                partitions {
                    compatible = "arm,arm-firmware-suite";
                };
            };

出自： buildroot-2020.11.1/output/build/linux-5.4.58/arch/arm/boot/dts/vexpress-v2p-ca9.dts

            buildroot-2020.11.1/output/build/linux-5.4.58/arch/arm/boot/dts/vexpress-v2m.dtsi

这里：

        ranges = <0 0 0x40000000 0x04000000>,              <1 0 0x44000000 0x04000000>,              <2 0 0x48000000 0x04000000>,              <3 0 0x4c000000 0x04000000>,              <7 0 0x10000000 0x00020000>; 每行第一个数字（0 1 2 3 7）是编号，表示不同range。对应  reg = <0 0x00000000 0x04000000>, 里的第一个数字 0 ranges = <编号   起始地址高32bit   起始地址低32bit   地址区域长度> reg = <编号    32bit偏移地址   地址区域长度>,