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u-boot启动的最后阶段获得linux对应os启动函数后执行它
do_bootm_linux
int do_bootm_linux(int flag, int argc, char * const argv[],
bootm_headers_t *images)
{
/* No need for those on ARM */
if (flag & BOOTM_STATE_OS_BD_T || flag & BOOTM_STATE_OS_CMDLINE)
return -1;
if (flag & BOOTM_STATE_OS_PREP) {
boot_prep_linux(images);//在里面会将bootargs的参数放在dts文件的chosen节点下，所以后面r2传递的是dtb而不是args
return 0;
}
if (flag & (BOOTM_STATE_OS_GO | BOOTM_STATE_OS_FAKE_GO)) {
boot_jump_linux(images, flag);
return 0;
}
boot_prep_linux(images);
boot_jump_linux(images, flag);//goto
return 0;
}
boot_jump_linux
static void boot_jump_linux(bootm_headers_t *images, int flag)
{
#ifdef CONFIG_ARM64
void (*kernel_entry)(void *fdt_addr, void *res0, void *res1,
void *res2);
int fake = (flag & BOOTM_STATE_OS_FAKE_GO);
kernel_entry = (void (*)(void *fdt_addr, void *res0, void *res1,
void *res2))images->ep;
debug("## Transferring control to Linux (at address %lx)...\n",
(ulong) kernel_entry);
bootstage_mark(BOOTSTAGE_ID_RUN_OS);
announce_and_cleanup(fake);//会打印Starting Kernel.....
if (!fake) {
do_nonsec_virt_switch();
kernel_entry(images->ft_addr, NULL, NULL, NULL);
}
#else
unsigned long machid = gd->bd->bi_arch_number;
char *s;
void (*kernel_entry)(int zero, int arch, uint params);
unsigned long r2;
int fake = (flag & BOOTM_STATE_OS_FAKE_GO);
kernel_entry = (void (*)(int, int, uint))images->ep;
s = getenv("machid");
if (s) {
if (strict_strtoul(s, 16, &machid)
#ifdef CONFIG_ARMV7_NONSEC
if (armv7_boot_nonsec()) {
armv7_init_nonsec();
secure_ram_addr(_do_nonsec_entry)(kernel_entry,
0, machid, r2);
} else
#endif
kernel_entry(0, machid, r2);/*跳到内核的第一行代码,kernel_entry就是内核的第一行代码标号，由于第一行代码是汇编，所以传的是r0,r1,r2 其中:
r1 :machid是机器的id，！如果使用设备树的话这个 machid 就无效了,
r2: 如果使用设备树的话是设备树地址否则bootargs (通过验证从网络启动时r2是dtb)
*/
}
#endif
}
setup_arch（由start_kernel调用）
void __init setup_arch(char **cmdline_p)
{
......
......
unflatten_device_tree();
......
}
unflatten_device_tree void __init unflatten_device_tree(void)
{
__unflatten_device_tree(initial_boot_params, &of_root,
early_init_dt_alloc_memory_arch);//解析平台设备树节点
/* Get pointer to "/chosen" and "/aliases" nodes for use everywhere */
of_alias_scan(early_init_dt_alloc_memory_arch);//解析chosen节点下的bootargs
}
__unflatten_device_tree static void __unflatten_device_tree(void *blob,
struct device_node **mynodes,
void * (*dt_alloc)(u64 size, u64 align))
{
unsigned long size;
int start;
void *mem;
pr_debug(" -> unflatten_device_tree()\n");
if (!blob) {
pr_debug("No device tree pointer\n");
return;
}
pr_debug("Unflattening device tree:\n");
pr_debug("magic: %08x\n", fdt_magic(blob));
pr_debug("size: %08x\n", fdt_totalsize(blob));
pr_debug("version: %08x\n", fdt_version(blob));
if (fdt_check_header(blob)) {
pr_err("Invalid device tree blob header\n");
return;
}
/* First pass, scan for size */
start = 0;
size = (unsigned long)unflatten_dt_node(blob, NULL, &start, NULL, NULL, 0, true);
size = ALIGN(size, 4);
pr_debug(" size is %lx, allocating...\n", size);
/* Allocate memory for the expanded device tree */
mem = dt_alloc(size + 4, __alignof__(struct device_node));//分配device_node内存
memset(mem, 0, size);
*(__be32 *)(mem + size) = cpu_to_be32(0xdeadbeef);
pr_debug(" unflattening %p...\n", mem);
/* Second pass, do actual unflattening */
start = 0;
unflatten_dt_node(blob, mem, &start, NULL, mynodes, 0, false);
if (be32_to_cpup(mem + size) != 0xdeadbeef)
pr_warning("End of tree marker overwritten: %08x\n",
be32_to_cpup(mem + size));
pr_debug(" |