/* kernel/drivers/okernel/drivers/of/fdt.c */
void __init unflatten_device_tree(void)
{
	__unflatten_device_tree(initial_boot_params, &of_allnodes,
				early_init_dt_alloc_memory_arch);

	/* Get pointer to "/chosen" and "/aliases" nodes for use everywhere */
	of_alias_scan(early_init_dt_alloc_memory_arch);
}

#define FDT_MAGIC	0xd00dfeed	/* 4: version, 4: total size */
#define FDT_FIRST_SUPPORTED_VERSION	0x10
#define FDT_LAST_SUPPORTED_VERSION	0x11
#define FDT_SW_MAGIC		(~FDT_MAGIC)

struct fdt_header {
	uint32_t magic;			 /* magic word FDT_MAGIC */
	uint32_t totalsize;		 /* total size of DT block */
	uint32_t off_dt_struct;		 /* offset to structure */
	uint32_t off_dt_strings;	 /* offset to strings */
	uint32_t off_mem_rsvmap;	 /* offset to memory reserve map */
	uint32_t version;		 /* format version */
	uint32_t last_comp_version;	 /* last compatible version */

	/* version 2 fields below */
	uint32_t boot_cpuid_phys;	 /* Which physical CPU id we're
					    booting on */
	/* version 3 fields below */
	uint32_t size_dt_strings;	 /* size of the strings block */

	/* version 17 fields below */
	uint32_t size_dt_struct;	 /* size of the structure block */
};
int fdt_check_header(const void *fdt)
{
	if (fdt_magic(fdt) == FDT_MAGIC) {
		/* Complete tree */
		if (fdt_version(fdt) < FDT_FIRST_SUPPORTED_VERSION)
			return -FDT_ERR_BADVERSION;
		if (fdt_last_comp_version(fdt) > FDT_LAST_SUPPORTED_VERSION)
			return -FDT_ERR_BADVERSION;
	} else if (fdt_magic(fdt) == FDT_SW_MAGIC) {
		/* Unfinished sequential-write blob */
		if (fdt_size_dt_struct(fdt) == 0)
			return -FDT_ERR_BADSTATE;
	} else {
		return -FDT_ERR_BADMAGIC;
	}

	return 0;
}

#define FDT_BEGIN_NODE	0x1		/* Start node: full name */
#define FDT_END_NODE	0x2		/* End node */
#define FDT_PROP	0x3		/* Property: name off,
					   size, content */
#define FDT_NOP		0x4		/* nop */
#define FDT_END		0x9
struct fdt_node_header {
	uint32_t tag;
	char name[0];
};

static inline const void *_fdt_offset_ptr(const void *fdt, int offset)
{
	return (const char *)fdt + fdt_off_dt_struct(fdt) + offset;
}

const char *fdt_get_name(const void *fdt, int nodeoffset, int *len)
{
	const struct fdt_node_header *nh = _fdt_offset_ptr(fdt, nodeoffset);
	int err;

	if (((err = fdt_check_header(fdt)) != 0)
	    || ((err = _fdt_check_node_offset(fdt, nodeoffset)) < 0))
			goto fail;

	if (len)
		*len = strlen(nh->name);

	return nh->name;

 fail:
	if (len)
		*len = err;
	return NULL;
}

	/* version 0x10 has a more compact unit name here instead of the full
	 * path. we accumulate the full path size using "fpsize", we'll rebuild
	 * it later. We detect this because the first character of the name is
	 * not '/'.
	 */
	if ((*pathp) != '/') {
		new_format = 1;
		if (fpsize == 0) {
			/* root node: special case. fpsize accounts for path
			 * plus terminating zero. root node only has '/', so
			 * fpsize should be 2, but we want to avoid the first
			 * level nodes to have two '/' so we use fpsize 1 here
			 */
			fpsize = 1;
			allocl = 2;
			l = 1;
			pathp = "";
		} else {
			/* account for '/' and path size minus terminal 0
			 * already in 'l'
			 */
			fpsize += l;
			allocl = fpsize;
		}
	}

struct fdt_property {
	uint32_t tag;
	uint32_t len;
	uint32_t nameoff;
	char data[0];
};
	/* process properties */
	for (offset = fdt_first_property_offset(blob, *poffset);
	     (offset >= 0);
	     (offset = fdt_next_property_offset(blob, offset))) {
		const char *pname;
		u32 sz;

		if (!(p = fdt_getprop_by_offset(blob, offset, &pname, &sz))) {
			offset = -FDT_ERR_INTERNAL;
			break;
		}

		if (pname == NULL) {
			pr_info("Can't find property name in list !\n");
			break;
		}
		if (strcmp(pname, "name") == 0)
			has_name = 1;
		pp = unflatten_dt_alloc(&mem, sizeof(struct property),
					__alignof__(struct property));
		if (allnextpp) {
			/* We accept flattened tree phandles either in
			 * ePAPR-style "phandle" properties, or the
			 * legacy "linux,phandle" properties.  If both
			 * appear and have different values, things
			 * will get weird.  Don't do that. */
			if ((strcmp(pname, "phandle") == 0) ||
			    (strcmp(pname, "linux,phandle") == 0)) {
				if (np->phandle == 0)
					np->phandle = be32_to_cpup(p);
			}
			/* And we process the "ibm,phandle" property
			 * used in pSeries dynamic device tree
			 * stuff */
			if (strcmp(pname, "ibm,phandle") == 0)
				np->phandle = be32_to_cpup(p);
			pp->name = (char *)pname;
			pp->length = sz;
			pp->value = (__be32 *)p;
			*prev_pp = pp;
			prev_pp = &pp->next;
		}
	}

*** kernel/drivers/bus/vexpress-config.c
static int __init vexpress_config_init(void)
{
	int err = 0;
	struct device_node *node;

	/* Need the config devices early, before the "normal" devices... */
	for_each_compatible_node(node, NULL, "arm,vexpress,config-bus") {
		err = vexpress_config_populate(node);
		if (err)
			break;
	}

	return err;
}
postcore_initcall(vexpress_config_init);

*** kernel/drivers/mfd/vexpress-sysreg.c
static void __iomem *vexpress_sysreg_base(void)
{
	if (!__vexpress_sysreg_base) {
		struct device_node *node = of_find_compatible_node(NULL, NULL,
				"arm,vexpress-sysreg");

		__vexpress_sysreg_base = of_iomap(node, 0);
	}

	WARN_ON(!__vexpress_sysreg_base);

	return __vexpress_sysreg_base;
}

*** kernel/drivers/of/base.c
struct device_node *of_find_compatible_node(struct device_node *from,
	const char *type, const char *compatible)
{
	struct device_node *np;
	unsigned long flags;

	raw_spin_lock_irqsave(&devtree_lock, flags);
	np = from ? from->allnext : of_allnodes;
	for (; np; np = np->allnext) {
		if (__of_device_is_compatible(np, compatible, type, NULL) &&
		    of_node_get(np))
			break;
	}
	of_node_put(from);
	raw_spin_unlock_irqrestore(&devtree_lock, flags);
	return np;
}
EXPORT_SYMBOL(of_find_compatible_node);

*** kernel/drivers/of/platform.c
int of_platform_populate(struct device_node *root,
			const struct of_device_id *matches,
			const struct of_dev_auxdata *lookup,
			struct device *parent)
{
	struct device_node *child;
	int rc = 0;

	root = root ? of_node_get(root) : of_find_node_by_path("/");
	if (!root)
		return -EINVAL;

	for_each_child_of_node(root, child) {
		rc = of_platform_bus_create(child, matches, lookup, parent, true);
		if (rc)
			break;
	}

	of_node_put(root);
	return rc;
}