blob: 5963925146a5df3fadbf29e33f6d5e995b5ff300 [file] [log] [blame]
#!/usr/bin/python
# SPDX-License-Identifier: GPL-2.0+
#
# Copyright (C) 2016 Google, Inc
# Written by Simon Glass <sjg@chromium.org>
#
from enum import IntEnum
import struct
import sys
from dtoc import fdt_util
import libfdt
from libfdt import QUIET_NOTFOUND
from u_boot_pylib import tools
from u_boot_pylib import tout
# This deals with a device tree, presenting it as an assortment of Node and
# Prop objects, representing nodes and properties, respectively. This file
# contains the base classes and defines the high-level API. You can use
# FdtScan() as a convenience function to create and scan an Fdt.
# This implementation uses a libfdt Python library to access the device tree,
# so it is fairly efficient.
# A list of types we support
class Type(IntEnum):
# Types in order from widest to narrowest
(BYTE, INT, STRING, BOOL, INT64) = range(5)
def needs_widening(self, other):
"""Check if this type needs widening to hold a value from another type
A wider type is one that can hold a wider array of information than
another one, or is less restrictive, so it can hold the information of
another type as well as its own. This is similar to the concept of
type-widening in C.
This uses a simple arithmetic comparison, since type values are in order
from widest (BYTE) to narrowest (INT64).
Args:
other: Other type to compare against
Return:
True if the other type is wider
"""
return self.value > other.value
def CheckErr(errnum, msg):
if errnum:
raise ValueError('Error %d: %s: %s' %
(errnum, libfdt.fdt_strerror(errnum), msg))
def BytesToValue(data):
"""Converts a string of bytes into a type and value
Args:
A bytes value (which on Python 2 is an alias for str)
Return:
A tuple:
Type of data
Data, either a single element or a list of elements. Each element
is one of:
Type.STRING: str/bytes value from the property
Type.INT: a byte-swapped integer stored as a 4-byte str/bytes
Type.BYTE: a byte stored as a single-byte str/bytes
"""
data = bytes(data)
size = len(data)
strings = data.split(b'\0')
is_string = True
count = len(strings) - 1
if count > 0 and not len(strings[-1]):
for string in strings[:-1]:
if not string:
is_string = False
break
for ch in string:
if ch < 32 or ch > 127:
is_string = False
break
else:
is_string = False
if is_string:
if count == 1:
return Type.STRING, strings[0].decode()
else:
return Type.STRING, [s.decode() for s in strings[:-1]]
if size % 4:
if size == 1:
return Type.BYTE, chr(data[0])
else:
return Type.BYTE, [chr(ch) for ch in list(data)]
val = []
for i in range(0, size, 4):
val.append(data[i:i + 4])
if size == 4:
return Type.INT, val[0]
else:
return Type.INT, val
class Prop:
"""A device tree property
Properties:
node: Node containing this property
offset: Offset of the property (None if still to be synced)
name: Property name (as per the device tree)
value: Property value as a string of bytes, or a list of strings of
bytes
type: Value type
"""
def __init__(self, node, offset, name, data):
self._node = node
self._offset = offset
self.name = name
self.value = None
self.bytes = bytes(data)
self.dirty = offset is None
if not data:
self.type = Type.BOOL
self.value = True
return
self.type, self.value = BytesToValue(bytes(data))
def RefreshOffset(self, poffset):
self._offset = poffset
def Widen(self, newprop):
"""Figure out which property type is more general
Given a current property and a new property, this function returns the
one that is less specific as to type. The less specific property will
be ble to represent the data in the more specific property. This is
used for things like:
node1 {
compatible = "fred";
value = <1>;
};
node1 {
compatible = "fred";
value = <1 2>;
};
He we want to use an int array for 'value'. The first property
suggests that a single int is enough, but the second one shows that
it is not. Calling this function with these two propertes would
update the current property to be like the second, since it is less
specific.
"""
if self.type.needs_widening(newprop.type):
# A boolean has an empty value: if it exists it is True and if not
# it is False. So when widening we always start with an empty list
# since the only valid integer property would be an empty list of
# integers.
# e.g. this is a boolean:
# some-prop;
# and it would be widened to int list by:
# some-prop = <1 2>;
if self.type == Type.BOOL:
self.type = Type.INT
self.value = [self.GetEmpty(self.type)]
if self.type == Type.INT and newprop.type == Type.BYTE:
if type(self.value) == list:
new_value = []
for val in self.value:
new_value += [chr(by) for by in val]
else:
new_value = [chr(by) for by in self.value]
self.value = new_value
self.type = newprop.type
if type(newprop.value) == list:
if type(self.value) != list:
self.value = [self.value]
if len(newprop.value) > len(self.value):
val = self.GetEmpty(self.type)
while len(self.value) < len(newprop.value):
self.value.append(val)
@classmethod
def GetEmpty(self, type):
"""Get an empty / zero value of the given type
Returns:
A single value of the given type
"""
if type == Type.BYTE:
return chr(0)
elif type == Type.INT:
return struct.pack('>I', 0);
elif type == Type.STRING:
return ''
else:
return True
def GetOffset(self):
"""Get the offset of a property
Returns:
The offset of the property (struct fdt_property) within the file
"""
self._node._fdt.CheckCache()
return self._node._fdt.GetStructOffset(self._offset)
def SetInt(self, val):
"""Set the integer value of the property
The device tree is marked dirty so that the value will be written to
the block on the next sync.
Args:
val: Integer value (32-bit, single cell)
"""
self.bytes = struct.pack('>I', val);
self.value = self.bytes
self.type = Type.INT
self.dirty = True
def SetData(self, bytes):
"""Set the value of a property as bytes
Args:
bytes: New property value to set
"""
self.bytes = bytes
self.type, self.value = BytesToValue(bytes)
self.dirty = True
def Sync(self, auto_resize=False):
"""Sync property changes back to the device tree
This updates the device tree blob with any changes to this property
since the last sync.
Args:
auto_resize: Resize the device tree automatically if it does not
have enough space for the update
Raises:
FdtException if auto_resize is False and there is not enough space
"""
if self.dirty:
node = self._node
tout.debug(f'sync {node.path}: {self.name}')
fdt_obj = node._fdt._fdt_obj
node_name = fdt_obj.get_name(node._offset)
if node_name and node_name != node.name:
raise ValueError("Internal error, node '%s' name mismatch '%s'" %
(node.path, node_name))
if auto_resize:
while fdt_obj.setprop(node.Offset(), self.name, self.bytes,
(libfdt.NOSPACE,)) == -libfdt.NOSPACE:
fdt_obj.resize(fdt_obj.totalsize() + 1024 +
len(self.bytes))
fdt_obj.setprop(node.Offset(), self.name, self.bytes)
else:
fdt_obj.setprop(node.Offset(), self.name, self.bytes)
self.dirty = False
def purge(self):
"""Set a property offset to None
The property remains in the tree structure and will be recreated when
the FDT is synced
"""
self._offset = None
self.dirty = True
class Node:
"""A device tree node
Properties:
parent: Parent Node
offset: Integer offset in the device tree (None if to be synced)
name: Device tree node tname
path: Full path to node, along with the node name itself
_fdt: Device tree object
subnodes: A list of subnodes for this node, each a Node object
props: A dict of properties for this node, each a Prop object.
Keyed by property name
"""
def __init__(self, fdt, parent, offset, name, path):
self._fdt = fdt
self.parent = parent
self._offset = offset
self.name = name
self.path = path
self.subnodes = []
self.props = {}
def GetFdt(self):
"""Get the Fdt object for this node
Returns:
Fdt object
"""
return self._fdt
def FindNode(self, name):
"""Find a node given its name
Args:
name: Node name to look for
Returns:
Node object if found, else None
"""
for subnode in self.subnodes:
if subnode.name == name:
return subnode
return None
def Offset(self):
"""Returns the offset of a node, after checking the cache
This should be used instead of self._offset directly, to ensure that
the cache does not contain invalid offsets.
"""
self._fdt.CheckCache()
return self._offset
def Scan(self):
"""Scan a node's properties and subnodes
This fills in the props and subnodes properties, recursively
searching into subnodes so that the entire tree is built.
"""
fdt_obj = self._fdt._fdt_obj
self.props = self._fdt.GetProps(self)
phandle = fdt_obj.get_phandle(self.Offset())
if phandle:
dup = self._fdt.phandle_to_node.get(phandle)
if dup:
raise ValueError(
f'Duplicate phandle {phandle} in nodes {dup.path} and {self.path}')
self._fdt.phandle_to_node[phandle] = self
offset = fdt_obj.first_subnode(self.Offset(), QUIET_NOTFOUND)
while offset >= 0:
sep = '' if self.path[-1] == '/' else '/'
name = fdt_obj.get_name(offset)
path = self.path + sep + name
node = Node(self._fdt, self, offset, name, path)
self.subnodes.append(node)
node.Scan()
offset = fdt_obj.next_subnode(offset, QUIET_NOTFOUND)
def Refresh(self, my_offset):
"""Fix up the _offset for each node, recursively
Note: This does not take account of property offsets - these will not
be updated.
"""
fdt_obj = self._fdt._fdt_obj
if self._offset != my_offset:
self._offset = my_offset
name = fdt_obj.get_name(self._offset)
if name and self.name != name:
raise ValueError("Internal error, node '%s' name mismatch '%s'" %
(self.path, name))
offset = fdt_obj.first_subnode(self._offset, QUIET_NOTFOUND)
for subnode in self.subnodes:
if subnode._offset is None:
continue
if subnode.name != fdt_obj.get_name(offset):
raise ValueError('Internal error, node name mismatch %s != %s' %
(subnode.name, fdt_obj.get_name(offset)))
subnode.Refresh(offset)
offset = fdt_obj.next_subnode(offset, QUIET_NOTFOUND)
if offset != -libfdt.FDT_ERR_NOTFOUND:
raise ValueError('Internal error, offset == %d' % offset)
poffset = fdt_obj.first_property_offset(self._offset, QUIET_NOTFOUND)
while poffset >= 0:
p = fdt_obj.get_property_by_offset(poffset)
prop = self.props.get(p.name)
if not prop:
raise ValueError("Internal error, node '%s' property '%s' missing, "
'offset %d' % (self.path, p.name, poffset))
prop.RefreshOffset(poffset)
poffset = fdt_obj.next_property_offset(poffset, QUIET_NOTFOUND)
def DeleteProp(self, prop_name):
"""Delete a property of a node
The property is deleted and the offset cache is invalidated.
Args:
prop_name: Name of the property to delete
Raises:
ValueError if the property does not exist
"""
CheckErr(self._fdt._fdt_obj.delprop(self.Offset(), prop_name),
"Node '%s': delete property: '%s'" % (self.path, prop_name))
del self.props[prop_name]
self._fdt.Invalidate()
def AddZeroProp(self, prop_name):
"""Add a new property to the device tree with an integer value of 0.
Args:
prop_name: Name of property
"""
self.props[prop_name] = Prop(self, None, prop_name,
tools.get_bytes(0, 4))
def AddEmptyProp(self, prop_name, len):
"""Add a property with a fixed data size, for filling in later
The device tree is marked dirty so that the value will be written to
the blob on the next sync.
Args:
prop_name: Name of property
len: Length of data in property
"""
value = tools.get_bytes(0, len)
self.props[prop_name] = Prop(self, None, prop_name, value)
def _CheckProp(self, prop_name):
"""Check if a property is present
Args:
prop_name: Name of property
Returns:
self
Raises:
ValueError if the property is missing
"""
if prop_name not in self.props:
raise ValueError("Fdt '%s', node '%s': Missing property '%s'" %
(self._fdt._fname, self.path, prop_name))
return self
def SetInt(self, prop_name, val):
"""Update an integer property int the device tree.
This is not allowed to change the size of the FDT.
The device tree is marked dirty so that the value will be written to
the blob on the next sync.
Args:
prop_name: Name of property
val: Value to set
"""
self._CheckProp(prop_name).props[prop_name].SetInt(val)
def SetData(self, prop_name, val):
"""Set the data value of a property
The device tree is marked dirty so that the value will be written to
the blob on the next sync.
Args:
prop_name: Name of property to set
val: Data value to set
"""
self._CheckProp(prop_name).props[prop_name].SetData(val)
def SetString(self, prop_name, val):
"""Set the string value of a property
The device tree is marked dirty so that the value will be written to
the blob on the next sync.
Args:
prop_name: Name of property to set
val: String value to set (will be \0-terminated in DT)
"""
if type(val) == str:
val = val.encode('utf-8')
self._CheckProp(prop_name).props[prop_name].SetData(val + b'\0')
def AddData(self, prop_name, val):
"""Add a new property to a node
The device tree is marked dirty so that the value will be written to
the blob on the next sync.
Args:
prop_name: Name of property to add
val: Bytes value of property
Returns:
Prop added
"""
prop = Prop(self, None, prop_name, val)
self.props[prop_name] = prop
return prop
def AddString(self, prop_name, val):
"""Add a new string property to a node
The device tree is marked dirty so that the value will be written to
the blob on the next sync.
Args:
prop_name: Name of property to add
val: String value of property
Returns:
Prop added
"""
val = bytes(val, 'utf-8')
return self.AddData(prop_name, val + b'\0')
def AddStringList(self, prop_name, val):
"""Add a new string-list property to a node
The device tree is marked dirty so that the value will be written to
the blob on the next sync.
Args:
prop_name: Name of property to add
val (list of str): List of strings to add
Returns:
Prop added
"""
out = b'\0'.join(bytes(s, 'utf-8') for s in val) + b'\0' if val else b''
return self.AddData(prop_name, out)
def AddInt(self, prop_name, val):
"""Add a new integer property to a node
The device tree is marked dirty so that the value will be written to
the blob on the next sync.
Args:
prop_name: Name of property to add
val: Integer value of property
Returns:
Prop added
"""
return self.AddData(prop_name, struct.pack('>I', val))
def Subnode(self, name):
"""Create new subnode for the node
Args:
name: name of node to add
Returns:
New subnode that was created
"""
path = self.path + '/' + name
return Node(self._fdt, self, None, name, path)
def AddSubnode(self, name):
"""Add a new subnode to the node, after all other subnodes
Args:
name: name of node to add
Returns:
New subnode that was created
"""
subnode = self.Subnode(name)
self.subnodes.append(subnode)
return subnode
def insert_subnode(self, name):
"""Add a new subnode to the node, before all other subnodes
This deletes other subnodes and sets their offset to None, so that they
will be recreated after this one.
Args:
name: name of node to add
Returns:
New subnode that was created
"""
# Deleting a node invalidates the offsets of all following nodes, so
# process in reverse order so that the offset of each node remains valid
# until deletion.
for subnode in reversed(self.subnodes):
subnode.purge(True)
subnode = self.Subnode(name)
self.subnodes.insert(0, subnode)
return subnode
def purge(self, delete_it=False):
"""Purge this node, setting offset to None and deleting from FDT"""
if self._offset is not None:
if delete_it:
CheckErr(self._fdt._fdt_obj.del_node(self.Offset()),
"Node '%s': delete" % self.path)
self._offset = None
self._fdt.Invalidate()
for prop in self.props.values():
prop.purge()
for subnode in self.subnodes:
subnode.purge(False)
def move_to_first(self):
"""Move the current node to first in its parent's node list"""
parent = self.parent
if parent.subnodes and parent.subnodes[0] == self:
return
for subnode in reversed(parent.subnodes):
subnode.purge(True)
new_subnodes = [self]
for subnode in parent.subnodes:
#subnode.purge(False)
if subnode != self:
new_subnodes.append(subnode)
parent.subnodes = new_subnodes
def Delete(self):
"""Delete a node
The node is deleted and the offset cache is invalidated.
Args:
node (Node): Node to delete
Raises:
ValueError if the node does not exist
"""
CheckErr(self._fdt._fdt_obj.del_node(self.Offset()),
"Node '%s': delete" % self.path)
parent = self.parent
self._fdt.Invalidate()
parent.subnodes.remove(self)
def Sync(self, auto_resize=False):
"""Sync node changes back to the device tree
This updates the device tree blob with any changes to this node and its
subnodes since the last sync.
Args:
auto_resize: Resize the device tree automatically if it does not
have enough space for the update
Returns:
True if the node had to be added, False if it already existed
Raises:
FdtException if auto_resize is False and there is not enough space
"""
added = False
if self._offset is None:
# The subnode doesn't exist yet, so add it
fdt_obj = self._fdt._fdt_obj
if auto_resize:
while True:
offset = fdt_obj.add_subnode(self.parent._offset, self.name,
(libfdt.NOSPACE,))
if offset != -libfdt.NOSPACE:
break
fdt_obj.resize(fdt_obj.totalsize() + 1024)
else:
offset = fdt_obj.add_subnode(self.parent._offset, self.name)
self._offset = offset
added = True
# Sync the existing subnodes first, so that we can rely on the offsets
# being correct. As soon as we add new subnodes, it pushes all the
# existing subnodes up.
for node in reversed(self.subnodes):
if node._offset is not None:
node.Sync(auto_resize)
# Sync subnodes in reverse so that we get the expected order. Each
# new node goes at the start of the subnode list. This avoids an O(n^2)
# rescan of node offsets.
num_added = 0
for node in reversed(self.subnodes):
if node.Sync(auto_resize):
num_added += 1
if num_added:
# Reorder our list of nodes to put the new ones first, since that's
# what libfdt does
old_count = len(self.subnodes) - num_added
subnodes = self.subnodes[old_count:] + self.subnodes[:old_count]
self.subnodes = subnodes
# Sync properties now, whose offsets should not have been disturbed,
# since properties come before subnodes. This is done after all the
# subnode processing above, since updating properties can disturb the
# offsets of those subnodes.
# Properties are synced in reverse order, with new properties added
# before existing properties are synced. This ensures that the offsets
# of earlier properties are not disturbed.
# Note that new properties will have an offset of None here, which
# Python cannot sort against int. So use a large value instead so that
# new properties are added first.
prop_list = sorted(self.props.values(),
key=lambda prop: prop._offset or 1 << 31,
reverse=True)
for prop in prop_list:
prop.Sync(auto_resize)
return added
def merge_props(self, src, copy_phandles):
"""Copy missing properties (except 'phandle') from another node
Args:
src (Node): Node containing properties to copy
copy_phandles (bool): True to copy phandle properties in nodes
Adds properties which are present in src but not in this node. Any
'phandle' property is not copied since this might result in two nodes
with the same phandle, thus making phandle references ambiguous.
"""
tout.debug(f'copy to {self.path}: {src.path}')
for name, src_prop in src.props.items():
done = False
if name not in self.props:
if copy_phandles or name != 'phandle':
self.props[name] = Prop(self, None, name, src_prop.bytes)
done = True
tout.debug(f" {name}{'' if done else ' - ignored'}")
def copy_node(self, src, copy_phandles=False):
"""Copy a node and all its subnodes into this node
Args:
src (Node): Node to copy
copy_phandles (bool): True to copy phandle properties in nodes
Returns:
Node: Resulting destination node
This works recursively, with copy_phandles being set to True for the
recursive calls
The new node is put before all other nodes. If the node already
exists, just its subnodes and properties are copied, placing them before
any existing subnodes. Properties which exist in the destination node
already are not copied.
"""
dst = self.FindNode(src.name)
if dst:
dst.move_to_first()
else:
dst = self.insert_subnode(src.name)
dst.merge_props(src, copy_phandles)
# Process in reverse order so that they appear correctly in the result,
# since copy_node() puts the node first in the list
for node in reversed(src.subnodes):
dst.copy_node(node, True)
return dst
def copy_subnodes_from_phandles(self, phandle_list):
"""Copy subnodes of a list of nodes into another node
Args:
phandle_list (list of int): List of phandles of nodes to copy
For each node in the phandle list, its subnodes and their properties are
copied recursively. Note that it does not copy the node itself, nor its
properties.
"""
# Process in reverse order, since new nodes are inserted at the start of
# the destination's node list. We want them to appear in order of the
# phandle list
for phandle in phandle_list.__reversed__():
parent = self.GetFdt().LookupPhandle(phandle)
tout.debug(f'adding template {parent.path} to node {self.path}')
for node in parent.subnodes.__reversed__():
dst = self.copy_node(node)
tout.debug(f'merge props from {parent.path} to {dst.path}')
self.merge_props(parent, False)
class Fdt:
"""Provides simple access to a flat device tree blob using libfdts.
Properties:
fname: Filename of fdt
_root: Root of device tree (a Node object)
name: Helpful name for this Fdt for the user (useful when creating the
DT from data rather than a file)
"""
def __init__(self, fname):
self._fname = fname
self._cached_offsets = False
self.phandle_to_node = {}
self.name = ''
if self._fname:
self.name = self._fname
self._fname = fdt_util.EnsureCompiled(self._fname)
with open(self._fname, 'rb') as fd:
self._fdt_obj = libfdt.Fdt(fd.read())
@staticmethod
def FromData(data, name=''):
"""Create a new Fdt object from the given data
Args:
data: Device-tree data blob
name: Helpful name for this Fdt for the user
Returns:
Fdt object containing the data
"""
fdt = Fdt(None)
fdt._fdt_obj = libfdt.Fdt(bytes(data))
fdt.name = name
return fdt
def LookupPhandle(self, phandle):
"""Look up a phandle
Args:
phandle: Phandle to look up (int)
Returns:
Node object the phandle points to
"""
return self.phandle_to_node.get(phandle)
def Scan(self, root='/'):
"""Scan a device tree, building up a tree of Node objects
This fills in the self._root property
Args:
root: Ignored
TODO(sjg@chromium.org): Implement the 'root' parameter
"""
self.phandle_to_node = {}
self._cached_offsets = True
self._root = self.Node(self, None, 0, '/', '/')
self._root.Scan()
def GetRoot(self):
"""Get the root Node of the device tree
Returns:
The root Node object
"""
return self._root
def GetNode(self, path):
"""Look up a node from its path
Args:
path: Path to look up, e.g. '/microcode/update@0'
Returns:
Node object, or None if not found
"""
node = self._root
parts = path.split('/')
if len(parts) < 2:
return None
if len(parts) == 2 and parts[1] == '':
return node
for part in parts[1:]:
node = node.FindNode(part)
if not node:
return None
return node
def Flush(self):
"""Flush device tree changes back to the file
If the device tree has changed in memory, write it back to the file.
"""
with open(self._fname, 'wb') as fd:
fd.write(self._fdt_obj.as_bytearray())
def Sync(self, auto_resize=False):
"""Make sure any DT changes are written to the blob
Args:
auto_resize: Resize the device tree automatically if it does not
have enough space for the update
Raises:
FdtException if auto_resize is False and there is not enough space
"""
self.CheckCache()
self._root.Sync(auto_resize)
self.Refresh()
def Pack(self):
"""Pack the device tree down to its minimum size
When nodes and properties shrink or are deleted, wasted space can
build up in the device tree binary.
"""
CheckErr(self._fdt_obj.pack(), 'pack')
self.Refresh()
def GetContents(self):
"""Get the contents of the FDT
Returns:
The FDT contents as a string of bytes
"""
return bytes(self._fdt_obj.as_bytearray())
def GetFdtObj(self):
"""Get the contents of the FDT
Returns:
The FDT contents as a libfdt.Fdt object
"""
return self._fdt_obj
def GetProps(self, node):
"""Get all properties from a node.
Args:
node: Full path to node name to look in.
Returns:
A dictionary containing all the properties, indexed by node name.
The entries are Prop objects.
Raises:
ValueError: if the node does not exist.
"""
props_dict = {}
poffset = self._fdt_obj.first_property_offset(node._offset,
QUIET_NOTFOUND)
while poffset >= 0:
p = self._fdt_obj.get_property_by_offset(poffset)
prop = Prop(node, poffset, p.name, p)
props_dict[prop.name] = prop
poffset = self._fdt_obj.next_property_offset(poffset,
QUIET_NOTFOUND)
return props_dict
def Invalidate(self):
"""Mark our offset cache as invalid"""
self._cached_offsets = False
def CheckCache(self):
"""Refresh the offset cache if needed"""
if self._cached_offsets:
return
self.Refresh()
def Refresh(self):
"""Refresh the offset cache"""
self._root.Refresh(0)
self._cached_offsets = True
def GetStructOffset(self, offset):
"""Get the file offset of a given struct offset
Args:
offset: Offset within the 'struct' region of the device tree
Returns:
Position of @offset within the device tree binary
"""
return self._fdt_obj.off_dt_struct() + offset
@classmethod
def Node(self, fdt, parent, offset, name, path):
"""Create a new node
This is used by Fdt.Scan() to create a new node using the correct
class.
Args:
fdt: Fdt object
parent: Parent node, or None if this is the root node
offset: Offset of node
name: Node name
path: Full path to node
"""
node = Node(fdt, parent, offset, name, path)
return node
def GetFilename(self):
"""Get the filename of the device tree
Returns:
String filename
"""
return self._fname
def FdtScan(fname):
"""Returns a new Fdt object"""
dtb = Fdt(fname)
dtb.Scan()
return dtb