一. 在linux中，對dtb檔案解析的整個過程式如下：

1）首先將從u-boot 傳遞過來的映像基地址和dtb 檔案映像基地址儲存通用暫存器r30,r31；
2）通過呼叫machine_init()、early_init_devtree()函式來獲取核心前期初始化所需的bootargs,cmd_line等系統引導引數；
3）呼叫start_kernel()、setup_arch()、unflatten_device_tree（）函式來解析dtb 檔案，構建一個由device_node 結構連線而成的單項鍊表，並使用全域性變數allnodes 指標來儲存這個連結串列的頭指標；如下在此函式執行過後，在記憶體中會存在一個如下的連結串列,後面所有的函式，如果需要從of tree結構上讀取裝置資料的，都將從這個連結串列中遍歷並讀取。

4）核心呼叫OF 提供的API 函式獲取allnodes連結串列資訊來初始化核心其他子系統、裝置等。（of_flatform_device）

 二、dts檔案首地址解析

在進行DTS檔案解析之前先要從bootm啟動命令中獲取dtb檔案所在的地址。而這一步的開始是從arch/powerpc/kernel/head_32.s檔案開始中的。

1、arch/powerpc/kernel/head_32.s

 * This is where the main kernel code starts.
 */
start_here:
/* ptr to current */
lisr2,[email protected]

orir2,r2,[email protected]
/* Set up for using our exception vectors */
/* ptr to phys current thread */
tophys(r4,r2)
addir4,r4,THREAD/* init task's THREAD */
CLR_TOP32(r4)
mtsprSPRN_SPRG_THREAD,r4
lir3,0
mtsprSPRN_SPRG_RTAS,r3/* 0 => not in RTAS */
/* stack */
lisr1,[email protected]
addir1,r1,[email protected]

lir0,0
stwur0,THREAD_SIZE-STACK_FRAME_OVERHEAD(r1)
/*
 * Do early platform-specific initialization,
 * and set up the MMU.
 */
mrr3,r31
mrr4,r30
blmachine_init  //在這個函式中
bl__save_cpu_setup
blMMU_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("/[email protected]");


DBG(" <- unflatten_device_tree()\n");
}

四. 將allnodes顯示在/proc/device-tree目錄下

start_kernel() --> 
#ifdef CONFIG_PROC_FS
proc_root_init(); --> 
#endif
#ifdef CONFIG_PROC_DEVICETREE
proc_device_tree_init(); --> 
#endif

proc_device_tree_add_node(root, proc_device_tree);

此時將在/proc/device-tree目錄下生成裝置節點
# ls -al /proc/device-tree

五. of_platform_bus_type的註冊/初始化 

-------------------------------------------------------------------
arch/powerpc/kernel/of_platform.c
struct bus_type of_platform_bus_type = {
       .uevent   = of_device_uevent,
};
EXPORT_SYMBOL(of_platform_bus_type);

static int __init of_bus_driver_init(void)
{
   return of_bus_type_init(&of_platform_bus_type, "of_platform");
}
postcore_initcall(of_bus_driver_init);

of_platform_bus_type匯流排註冊完畢。
此時/sys/bus/目錄下將會有of_platform

六. 將allnodes裝置節點新增到匯流排of_platform_bus_type上

-------------------------------------------------------------------
arch/powerpc/platform/85xx/mpc85Xx_ads.c

static int __init declare_of_platform_devices(void)
{
of_platform_bus_probe(NULL, of_bus_ids, NULL);


return 0;
}
machine_device_initcall(mpc85xx_ads, declare_of_platform_devices);

declare_of_platform_devices() --> of_platform_bus_probe(NULL, of_bus_ids, NULL)

arch/powerpc/kernel/of_platform.c
遍歷第一步中在記憶體中生成連結串列的所有soc的子節點，將所有的soc子節點裝置新增到of_platform匯流排。
int of_platform_bus_probe(struct device_node *root,
 const struct of_device_id *matches,
 struct device *parent)
{
struct device_node *child;
struct of_device *dev;
int rc = 0;


if (matches == NULL)
matches = of_default_bus_ids;
if (matches == OF_NO_DEEP_PROBE)
return -EINVAL;
if (root == NULL)
root = of_find_node_by_path("/");
else
of_node_get(root);


pr_debug("of_platform_bus_probe()\n");
pr_debug(" starting at: %s\n", root->full_name);


/* Do a self check of bus type, if there's a match, create
* children
*/
if (of_match_node(matches, root)) {
pr_debug(" root match, create all sub devices\n");
dev = of_platform_device_create(root, NULL, parent);
if (dev == NULL) {
rc = -ENOMEM;
goto bail;
}
pr_debug(" create all sub busses\n");
rc = of_platform_bus_create(root, matches, &dev->dev);
goto bail;
}
for_each_child_of_node(root, child) {
if (!of_match_node(matches, child))
continue;


pr_debug("  match: %s\n", child->full_name);
dev = of_platform_device_create(child, NULL, parent);
if (dev == NULL)
rc = -ENOMEM;
else
rc = of_platform_bus_create(child, matches, &dev->dev);
if (rc) {
of_node_put(child);
break;
}
}
 bail:
of_node_put(root);
return rc;
}
EXPORT_SYMBOL(of_platform_bus_probe);
--> of_platform_device_create--> of_device_register() --> device_add()

of_platform總線上的所有裝置新增完畢，e0024000.ethernet，e0024520.mdio等裝置現在都在總線上。至此裝置節點將出現在/sys/devices/platform/

七、例項

 1、mdio匯流排的註冊

/driver/net/phy_device.c

subsys_initcall(phy_init)
phy_init --> mdio_bus_init --> bus_register(&mdio_bus_type)

匯流排註冊後，在總線上註冊了一個預設的phy的驅動 genphy_driver：

.phy_id      = 0xffffffff,
.phy_id_mask = 0xffffffff,
.name        = "Generic phy",

mdio匯流排註冊完畢。
/sys/bus/mdio

2、 mdio總線上驅動的新增
--------------------------------------------

/driver/net/phy/marvell.c
module_init(marvell_init)
marvell_init() --> 
phy_driver_register(&marvell_drivers[i]) --> 
driver_register()

前面第三步，註冊mdio匯流排後，已經添加了一個預設的phy的驅動，現在要將所有的phy驅動新增到總線上，這裡將所有的marvell的phy都新增。

這步過後，核心的/sys/bus/mdio/driver裡面就有了各種phy的驅動，但這時還沒有和具體的裝置繫結。

3、 of_platform總線上mdio裝置驅動（該驅動的目的是在mdio總線上新增phy裝置）的新增，並繫結裝置：e0024520.mdio和e0025520.mdio

/driver/net/fsl_pq_mdio.c
module_init(fsl_pq_mdio_init)
fsl_pq_mdio_init --> of_register_platform_driver(&fsl_pq_mdio_driver) --> of_register_driver --> driver_register --> bus_add_driver --> driver_attach

遍歷整個of_platform匯流排，尋找與之相匹配的裝置，找到e0024520.mdio
driver_attach --> __driver_attach --> driver_match_device
將driver的match_table裡的資訊和dev_nod中的做比較，若符合就進入driver的probe，也就是fsl_pq_mdio_probe。

現在of_platform總線上的裝置e0024520.mdio和e0025520.mdio已經綁定了驅動。
4、 mdio總線上的裝置的新增，尋找並繫結相應的驅動。
/driver/net/fsl_pq_mdio.c
fsl_pq_mdio_probe --> of_mdiobus_register --> phy_device_register --> device_register(&phydev->dev) --> device_add --> bus_probe_device --> device_attach -->bus_for_each_drv
掃描mdio總線上的所有的驅動，若找到匹配的，就繫結，並probe。
__device_attach --> driver_probe_device --> really_probe --> phy_probe

將所有的phy和tbi-phy的裝置都新增到mdio總線上，並且兩個phy裝置和兩個tbi-phy裝置都會根據其自己的phyID找到各自的驅動