1, chosen節點bootargs屬性

uboot程式碼解析ramdisk/initramfs映象，然後設定環境變數setenv("bootargs")，呼叫fdt_setprop（common/fdt_support.c）設定chosen節點的bootargs屬性。

kernel從r2暫存器拿到fdt後，通過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程式碼設定的實體地址。

2，chosen節點linux,initrd-start，linux,initrd-end屬性

uboot程式碼解析ramdisk/initramfs映象，呼叫fdt_setprop（common/fdt_support.c）設定chosen節點的linux,initrd-start ，linux,initrd-end屬性（common/fdt_support.c：fdt_getprop(fdt, nodeoffset, "linux,initrd-start", NULL); fdt_setprop）。

kernel從r2暫存器拿到fdt後，通過early_init_dt_scan_chosen->early_init_dt_check_for_initrd(node);

裝置樹：

        chosen {  
                bootargs = "console=ttyAMA0,115200 loglevel=7 panic=3 isolcpus=1
                linux,initrd-start = <0x27a35000>; //uboot程式碼設定的實體地址
                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_FLATTREE
void __init early_init_dt_setup_initrd_arch(unsigned long start, unsigned long end)
{
	phys_initrd_start = start; //實體地址
	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);//得到虛擬地址
		initrd_end = initrd_start + phys_initrd_size;