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# Copyright (C) 2016 Google, Inc
# Written by Simon Glass <>
# SPDX-License-Identifier: GPL-2.0+
import struct
import sys
import fdt
from fdt import Fdt, NodeBase, PropBase
import fdt_util
import libfdt
# This deals with a device tree, presenting it as a list of Node and Prop
# objects, representing nodes and properties, respectively.
# This implementation uses a libfdt Python library to access the device tree,
# so it is fairly efficient.
def CheckErr(errnum, msg):
if errnum:
raise ValueError('Error %d: %s: %s' %
(errnum, libfdt.fdt_strerror(errnum), msg))
class Prop(PropBase):
"""A device tree property
name: Property name (as per the device tree)
value: Property value as a string of bytes, or a list of strings of
type: Value type
def __init__(self, node, offset, name, bytes):
PropBase.__init__(self, node, offset, name)
self.bytes = bytes
if not bytes:
self.type = fdt.TYPE_BOOL
self.value = True
self.type, self.value = self.BytesToValue(bytes)
def GetOffset(self):
"""Get the offset of a property
The offset of the property (struct fdt_property) within the file
return self._node._fdt.GetStructOffset(self._offset)
class Node(NodeBase):
"""A device tree node
offset: Integer offset in the device tree
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, offset, name, path):
NodeBase.__init__(self, fdt, offset, name, path)
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.
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.
self.props = self._fdt.GetProps(self)
offset = libfdt.fdt_first_subnode(self._fdt.GetFdt(), self.Offset())
while offset >= 0:
sep = '' if self.path[-1] == '/' else '/'
name = libfdt.Name(self._fdt.GetFdt(), offset)
path = self.path + sep + name
node = Node(self._fdt, offset, name, path)
offset = libfdt.fdt_next_subnode(self._fdt.GetFdt(), offset)
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.
if self._offset != my_offset:
#print '%s: %d -> %d\n' % (self.path, self._offset, my_offset)
self._offset = my_offset
offset = libfdt.fdt_first_subnode(self._fdt.GetFdt(), self._offset)
for subnode in self.subnodes:
offset = libfdt.fdt_next_subnode(self._fdt.GetFdt(), offset)
def DeleteProp(self, prop_name):
"""Delete a property of a node
The property is deleted and the offset cache is invalidated.
prop_name: Name of the property to delete
ValueError if the property does not exist
CheckErr(libfdt.fdt_delprop(self._fdt.GetFdt(), self.Offset(), prop_name),
"Node '%s': delete property: '%s'" % (self.path, prop_name))
del self.props[prop_name]
class FdtNormal(Fdt):
"""Provides simple access to a flat device tree blob using libfdt.
_fdt: Device tree contents (bytearray)
_cached_offsets: True if all the nodes have a valid _offset property,
False if something has changed to invalidate the offsets
def __init__(self, fname):
Fdt.__init__(self, fname)
self._cached_offsets = False
if self._fname:
self._fname = fdt_util.EnsureCompiled(self._fname)
with open(self._fname) as fd:
self._fdt = bytearray(
def GetFdt(self):
"""Get the contents of the FDT
The FDT contents as a string of bytes
return self._fdt
def Flush(self):
"""Flush device tree changes back to the file"""
with open(self._fname, 'wb') as fd:
def Pack(self):
"""Pack the device tree down to its minimum size"""
CheckErr(libfdt.fdt_pack(self._fdt), 'pack')
fdt_len = libfdt.fdt_totalsize(self._fdt)
del self._fdt[fdt_len:]
def GetProps(self, node):
"""Get all properties from a node.
node: Full path to node name to look in.
A dictionary containing all the properties, indexed by node name.
The entries are Prop objects.
ValueError: if the node does not exist.
props_dict = {}
poffset = libfdt.fdt_first_property_offset(self._fdt, node._offset)
while poffset >= 0:
dprop, plen = libfdt.fdt_get_property_by_offset(self._fdt, poffset)
prop = Prop(node, poffset, libfdt.String(self._fdt, dprop.nameoff),
props_dict[] = prop
poffset = libfdt.fdt_next_property_offset(self._fdt, poffset)
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:
self._cached_offsets = True
def Refresh(self):
"""Refresh the offset cache"""
def GetStructOffset(self, offset):
"""Get the file offset of a given struct offset
offset: Offset within the 'struct' region of the device tree
Position of @offset within the device tree binary
return libfdt.fdt_off_dt_struct(self._fdt) + offset
def Node(self, fdt, offset, name, path):
"""Create a new node
This is used by Fdt.Scan() to create a new node using the correct
fdt: Fdt object
offset: Offset of node
name: Node name
path: Full path to node
node = Node(fdt, offset, name, path)
return node