#!/usr/bin/python
#
# Copyright (C) 2016 Google, Inc
# Written by Simon Glass <sjg@chromium.org>
#
# SPDX-License-Identifier: GPL-2.0+
#
import struct
import sys
import fdt_util
# 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. Most of the
# implementation is in the FdtFallback and FdtNormal subclasses. See
# fdt_select.py for how to create an Fdt object.
# A list of types we support
(TYPE_BYTE, TYPE_INT, TYPE_STRING, TYPE_BOOL) = range(4)
def CheckErr(errnum, msg):
if errnum:
raise ValueError('Error %d: %s: %s' %
(errnum, libfdt.fdt_strerror(errnum), msg))
class PropBase:
"""A device tree property
Properties:
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):
self._node = node
self._offset = offset
self.name = name
self.value = None
def GetPhandle(self):
"""Get a (single) phandle value from a property
Gets the phandle valuie from a property and returns it as an integer
"""
return fdt_util.fdt32_to_cpu(self.value[:4])
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 newprop.type < self.type:
self.type = newprop.type
if type(newprop.value) == list and type(self.value) != list:
self.value = [self.value]
if type(self.value) == list and len(newprop.value) > len(self.value):
val = self.GetEmpty(self.type)
while len(self.value) < len(newprop.value):
self.value.append(val)
def BytesToValue(self, bytes):
"""Converts a string of bytes into a type and value
Args:
A string containing bytes
Return:
A tuple:
Type of data
Data, either a single element or a list of elements. Each element
is one of:
TYPE_STRING: string value from the property
TYPE_INT: a byte-swapped integer stored as a 4-byte string
TYPE_BYTE: a byte stored as a single-byte string
"""
size = len(bytes)
strings = bytes.split('\0')
is_string = True
count = len(strings) - 1
if count > 0 and not strings[-1]:
for string in strings[:-1]:
if not string:
is_string = False
break
for ch in string:
if ch < ' ' or ch > '~':
is_string = False
break
else:
is_string = False
if is_string:
if count == 1:
return TYPE_STRING, strings[0]
else:
return TYPE_STRING, strings[:-1]
if size % 4:
if size == 1:
return TYPE_BYTE, bytes[0]
else:
return TYPE_BYTE, list(bytes)
val = []
for i in range(0, size, 4):
val.append(bytes[i:i + 4])
if size == 4:
return TYPE_INT, val[0]
else:
return TYPE_INT, val
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
This can be implemented by subclasses.
Returns:
The offset of the property (struct fdt_property) within the
file, or None if not known.
"""
return None
class NodeBase:
"""A device tree node
Properties:
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):
self._fdt = fdt
self._offset = offset
self.name = name
self.path = path
self.subnodes = []
self.props = {}
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 Scan(self):
"""Scan the subnodes of a node
This should be implemented by subclasses
"""
raise NotImplementedError()
def DeleteProp(self, prop_name):
"""Delete a property of a node
This should be implemented by subclasses
Args:
prop_name: Name of the property to delete
"""
raise NotImplementedError()
class Fdt:
"""Provides simple access to a flat device tree blob.
Properties:
fname: Filename of fdt
_root: Root of device tree (a Node object)
"""
def __init__(self, fname):
self._fname = fname
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._root = self.Node(self, 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
for part in path.split('/')[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.
Subclasses can implement this if needed.
"""
pass
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. Subclasses can implement this
to remove that spare space.
"""
pass