uboot傳遞initrd(initramfs or ramdisk) 到kernel的兩種方式
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;