uboot传递initrd(initramfs or ramdisk) 到kernel的两种方式

1, chosen节点bootargs属性

uboot代码解析ramdisk/initramfs镜像，然后设置环境变量setenv("bootargs")，调用fdt_setprop（common/fdt_support.c）设置chosen节点的bootargs属性。

kernel从r2寄存器拿到fdt后，通过early_init_dt_scan_chosen->of_get_flat_dt_prop(node, "bootargs", &l)解析得到bootargs。

eg，rdinit=/sbin/init rw console=ttyAMA0,115200n earlyprintk loglevel=4 mem=0x77ede000,@0x00000000 vmalloc=512M initrd=0x6000000,34190640 

0x6000000是uboot代码设置的物理地址。

2，chosen节点linux,initrd-start，linux,initrd-end属性

uboot代码解析ramdisk/initramfs镜像，调用fdt_setprop（common/fdt_support.c）设置chosen节点的linux,initrd-start ，linux,initrd-end属性（common/fdt_support.c：fdt_getprop(fdt, nodeoffset, "linux,initrd-start", NULL); fdt_setprop）。

kernel从r2寄存器拿到fdt后，通过early_init_dt_scan_chosen->early_init_dt_check_for_initrd(node);

设备树：

        chosen {  
                bootargs = "console=ttyAMA0,115200 loglevel=7 panic=3 isolcpus=1
                linux,initrd-start = <0x27a35000>; //uboot代码设置的物理地址
                linux,initrd-end  = <0x27fffae8>;
                rsr = <0x2>;      
                crtm_partition = "primary";

#ifdef CONFIG_BLK_DEV_INITRD/** * early_init_dt_check_for_initrd - Decode initrd location from flat tree * @node: reference to node containing initrd location ('chosen') */void __init early_init_dt_check_for_initrd(unsigned long node){unsigned long start, end, len;__be32 *prop;pr_debug("Looking for initrd properties... ");prop = of_get_flat_dt_prop(node, "linux,initrd-start", &len);if (!prop)return;start = of_read_ulong(prop, len/4);prop = of_get_flat_dt_prop(node, "linux,initrd-end", &len);if (!prop)return;end = of_read_ulong(prop, len/4);early_init_dt_setup_initrd_arch(start, end);pr_debug("initrd_start=0x%lx  initrd_end=0x%lx\n", start, end);}

#ifdef CONFIG_OF_FLATTREEvoid __init early_init_dt_setup_initrd_arch(unsigned long start, unsigned long end){phys_initrd_start = start; //物理地址phys_initrd_size = end - start;}#endif /* CONFIG_OF_FLATTREE */

arm_memblock_init:if (phys_initrd_size) {memblock_reserve(phys_initrd_start, phys_initrd_size);/* Now convert initrd to virtual addresses */initrd_start = __phys_to_virt(phys_initrd_start);//得到虚拟地址initrd_end = initrd_start + phys_initrd_size;