一. 在linux中，对dtb文件解析的整个过程序如下：1）首先将从u-boot 传递过来的映像基地址和dtb 文件映像基地址保存通用寄存器r30,r31；
2）通过调用machine_init()、early_init_devtree()函数来获取内核前期初始化所需的bootargs,cmd_line等系统引导参数；
3）调用start_kernel()、setup_arch()、unflatten_device_tree（）函数来解析dtb 文件，构建一个由device_node 结构连接而成的单项链表，并使用全局变量allnodes 指针来保存这个链表的头指针；如下在此函数执行过后，在内存中会存在一个如下的链表,后面所有的函数，如果需要从of tree结构上读取设备资料的，都将从这个链表中遍历并读取。
4）内核调用OF 提供的API 函数获取allnodes链表信息来初始化内核其他子系统、设备等。（of_flatform_device）
二、dts文件首地址解析在进行DTS文件解析之前先要从bootm启动命令中获取dtb文件所在的地址。而这一步的开始是从arch/powerpc/kernel/head_32.s文件开始中的。
1、arch/powerpc/kernel/head_32.s
* This is where the main kernel code starts.
*/
start_here:
/* ptr to current */
lis
r2,init_task@h
ori
r2,r2,init_task@l
/* Set up for using our exception vectors */
/* ptr to phys current thread */
tophys(r4,r2)
addi
r4,r4,THREAD
/* init task's THREAD */
CLR_TOP32(r4)
mtspr
SPRN_SPRG_THREAD,r4
li
r3,0
mtspr
SPRN_SPRG_RTAS,r3
/* 0 => not in RTAS */
/* stack */
lis
r1,init_thread_union@ha
addi
r1,r1,init_thread_union@l
li
r0,0
stwu
r0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
/*
* Do early platform-specific initialization,
* and set up the MMU.
*/
mr
r3,r31
mr
r4,r30
bl
machine_init //在这个函数中
bl
__save_cpu_setup
bl
MMU_init
notrace void __init machine_init(unsigned long dt_ptr)
{
lockdep_init();
/* Enable early debugging if any specified (see udbg.h) */
udbg_early_init();
/* Do some early initialization based on the flat device tree */
early_init_devtree(__va(dt_ptr));
probe_machine();
setup_kdump_trampoline();
#ifdef CONFIG_6xx
if (cpu_has_feature(CPU_FTR_CAN_DOZE) ||
cpu_has_feature(CPU_FTR_CAN_NAP))
ppc_md.power_save = ppc6xx_idle;
#endif
#ifdef CONFIG_E500
if (cpu_has_feature(CPU_FTR_CAN_DOZE) ||
cpu_has_feature(CPU_FTR_CAN_NAP))
ppc_md.power_save = e500_idle;
#endif
if (ppc_md.progress)
ppc_md.progress("id mach(): done", 0x200);
}
void __init early_init_devtree(void *params)
{
phys_addr_t limit;
DBG(" -> early_init_devtree(%p)\n", params);
/* Setup flat device-tree pointer */
initial_boot_params = params;
#ifdef CONFIG_PPC_RTAS
/* Some machines might need RTAS info for debugging, grab it now. */
of_scan_flat_dt(early_init_dt_scan_rtas, NULL);
#endif
#ifdef CONFIG_PHYP_DUMP
/* scan tree to see if dump occured during last boot */
of_scan_flat_dt(early_init_dt_scan_phyp_dump, NULL);
#endif
/* Retrieve various informations from the /chosen node of the
* device-tree, including the platform type, initrd location and
* size, TCE reserve, and more ...
*/
of_scan_flat_dt(early_init_dt_scan_chosen, NULL);
/* Scan memory nodes and rebuild LMBs */
lmb_init();
of_scan_flat_dt(early_init_dt_scan_root, NULL);
of_scan_flat_dt(early_init_dt_scan_memory, NULL);
/* Save command line for /proc/cmdline and then parse parameters */
strlcpy(boot_command_line, cmd_line, COMMAND_LINE_SIZE);
parse_early_param();
/* Reserve LMB regions used by kernel, initrd, dt, etc... */
lmb_reserve(PHYSICAL_START, __pa(klimit) - PHYSICAL_START);
/* If relocatable, reserve first 32k for interrupt vectors etc. */
if (PHYSICAL_START > MEMORY_START)
lmb_reserve(MEMORY_START, 0x8000);
reserve_kdump_trampoline();
reserve_crashkernel();
early_reserve_mem();
phyp_dump_reserve_mem();
limit = memory_limit;
if (! limit) {
phys_addr_t memsize;
/* Ensure that total memory size is page-aligned, because
* otherwise mark_bootmem() gets upset. */
lmb_analyze();
memsize = lmb_phys_mem_size();
if ((memsize & PAGE_MASK) != memsize)
limit = memsize & PAGE_MASK;
}
lmb_enforce_memory_limit(limit);
lmb_analyze();
lmb_dump_all();
DBG("Phys. mem: %llx\n", lmb_phys_mem_size());
/* We may need to relocate the flat tree, do it now.
* FIXME .. and the initrd too? */
move_device_tree();
DBG("Scanning CPUs ...\n");
/* Retreive CPU related informations from the flat tree
* (altivec support, boot CPU ID, ...)
*/
of_scan_flat_dt(early_init_dt_scan_cpus, NULL);
DBG(" <- early_init_devtree()\n");
}
三、解析main.c-------------->arch/pwerpc/kernel/setup_32.c-------------->arch/powerpc/kernel/prom.c
start_kernel()------>setup_arch()---------->unflatten_device_tree（）
/**
* unflattens the device-tree passed by the firmware, creating the
* tree of struct device_node. It also fills the "name" and "type"
* pointers of the nodes so the normal device-tree walking functions
* can be used (this used to be done by finish_device_tree)
*/
void __init unflatten_device_tree(void)
{
unsigned long start, mem, size;
struct device_node **allnextp = &allnodes;
DBG(" -> unflatten_device_tree()\n");
/* First pass, scan for size */
start = ((unsigned long)initial_boot_params) +
initial_boot_params->off_dt_struct;
size = unflatten_dt_node(0, &start, NULL, NULL, 0);
size = (size | 3) + 1;
DBG(" size is %lx, allocating...\n", size);
/* Allocate memory for the expanded device tree */
mem = lmb_alloc(size + 4, __alignof__(struct device_node));
mem = (unsigned long) __va(mem);
((u32 *)mem)[size / 4] = 0xdeadbeef;
DBG(" unflattening %lx...\n", mem);
/* Second pass, do actual unflattening */
start = ((unsigned long)initial_boot_params) +
initial_boot_params->off_dt_struct;
unflatten_dt_node(mem, &start, NULL, &allnextp, 0);
if (*((u32 *)start) != OF_DT_END)
printk(KERN_WARNING "Weird tag at end of tree: %08x\n", *((u32 *)start));
if (((u32 *)mem)[size / 4] != 0xdeadbeef)
printk(KERN_WARNING "End of tree marker overwritten: %08x\n",
((u32 *)mem)[size / 4] );
*allnextp = NULL;
/* Get pointer to OF "/chosen" node for use everywhere */
of_chosen = of_find_node_by_path("/chosen");
if (of_chosen == NULL)
of_chosen = of_find_node_by_path("/chosen@0");
DBG(" <- unflatten_device_tree()\n");
} |
