setup_arch(1) - setup_machine_fdt()

We will focus on device tree initialization in this article

First, take a look of setup_arch() -> setup_machine_fdt()

 static void __init setup_machine_fdt(phys_addr_t dt_phys)
 {
         void *dt_virt = fixmap_remap_fdt(dt_phys);
 
         if (!dt_virt || !early_init_dt_scan(dt_virt)) {
                 pr_crit("\n"
                         "Error: invalid device tree blob at physical address %pa (virtual address 0x%p)\n"
                         "The dtb must be 8-byte aligned and must not exceed 2 MB in size\n"
                         "\nPlease check your bootloader.",
                         &dt_phys, dt_virt);
 
                 while (true)
                         cpu_relax();
         }
 
         dump_stack_set_arch_desc("%s (DT)", of_flat_dt_get_machine_name());
 }

1. fixmap_remap_fdt(): 找到device tree的virtual addr
2. early_init_dt_scan(dt_virt): 為之後的DTB scan 做準備, 並進行參數傳遞

3. dump_stack_set_arch_desc(): 印出hardware name, 並把stack dump出來

由 2 進一步從early_init_dt_scan -> early_init_dt_scan_nodes() 看

 void __init early_init_dt_scan_nodes(void)
 {
         /* Retrieve various information from the /chosen node */
         of_scan_flat_dt(early_init_dt_scan_chosen, boot_command_line);
 
         /* Initialize {size,address}-cells info */
         of_scan_flat_dt(early_init_dt_scan_root, NULL);
 
         /* Setup memory, calling early_init_dt_add_memory_arch */
         of_scan_flat_dt(early_init_dt_scan_memory, NULL);
 }

第一個of_scan_flat_dt: scan /chosen node, save bootargs to boot_command_line, 還處理initrd相關的property, 存到initrd_start, initrd_end這兩個global variables中

第二個of_scan_flat_dt: scan root node, 取得 {size, addr}-cells 的資訊, 並存到dt_root_size_cells 和 dt_root_addr_cells global variables中

第三個of_scan_flat_dt: scan DTB中的memory node, 並把相關的資訊存入meminfo, meminfo是global variable, 保存系統的memory相關的資訊