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dm: Add a library to provide simple device-tree access

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This Python library provides a way to access the contents of the device
tree. It uses fdtget, so is inefficient for larger device tree files.

Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass 2016-07-04 11:58:08 -06:00
parent 39782afb1a
commit ec564b47da
3 changed files with 294 additions and 0 deletions
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1
tools/dtoc/.gitignore vendored Normal file
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*.pyc

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tools/dtoc/fdt_fallback.py Normal file
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#!/usr/bin/python
#
# Copyright (C) 2016 Google, Inc
# Written by Simon Glass <sjg@chromium.org>
#
# SPDX-License-Identifier: GPL-2.0+
#
import command
import fdt_util
import sys
# This deals with a device tree, presenting it as a list of Node and Prop
# objects, representing nodes and properties, respectively.
#
# This implementation uses the fdtget tool to access the device tree, so it
# is not very efficient for larger trees. The tool is called once for each
# node and property in the tree.
class Prop:
"""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, name, byte_list_str):
self.name = name
self.value = None
if not byte_list_str.strip():
self.type = fdt_util.TYPE_BOOL
return
bytes = [chr(int(byte, 16)) for byte in byte_list_str.strip().split(' ')]
self.type, self.value = fdt_util.BytesToValue(''.join(bytes))
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 = newprop.value
class Node:
"""A device tree node
Properties:
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, name, path):
self.name = name
self.path = path
self._fdt = fdt
self.subnodes = []
self.props = {}
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.
"""
for name, byte_list_str in self._fdt.GetProps(self.path).iteritems():
prop = Prop(name, byte_list_str)
self.props[name] = prop
for name in self._fdt.GetSubNodes(self.path):
sep = '' if self.path[-1] == '/' else '/'
path = self.path + sep + name
node = Node(self._fdt, name, path)
self.subnodes.append(node)
node.Scan()
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):
"""Scan a device tree, building up a tree of Node objects
This fills in the self._root property
"""
self._root = Node(self, '/', '/')
self._root.Scan()
def GetRoot(self):
"""Get the root Node of the device tree
Returns:
The root Node object
"""
return self._root
def GetSubNodes(self, node):
"""Returns a list of sub-nodes of a given node
Args:
node: Node name to return children from
Returns:
List of children in the node (each a string node name)
Raises:
CmdError: if the node does not exist.
"""
out = command.Output('fdtget', self.fname, '-l', node)
return out.strip().splitlines()
def GetProps(self, node, convert_dashes=False):
"""Get all properties from a node
Args:
node: full path to node name to look in
convert_dashes: True to convert - to _ in node names
Returns:
A dictionary containing all the properties, indexed by node name.
The entries are simply strings - no decoding of lists or numbers
is done.
Raises:
CmdError: if the node does not exist.
"""
out = command.Output('fdtget', self.fname, node, '-p')
props = out.strip().splitlines()
props_dict = {}
for prop in props:
name = prop
if convert_dashes:
prop = re.sub('-', '_', prop)
props_dict[prop] = self.GetProp(node, name)
return props_dict
def GetProp(self, node, prop, default=None, typespec=None):
"""Get a property from a device tree.
This looks up the given node and property, and returns the value as a
string,
If the node or property does not exist, this will return the default
value.
Args:
node: Full path to node to look up.
prop: Property name to look up.
default: Default value to return if nothing is present in the fdt,
or None to raise in this case. This will be converted to a
string.
typespec: Type character to use (None for default, 's' for string)
Returns:
string containing the property value.
Raises:
CmdError: if the property does not exist and no default is provided.
"""
args = [self.fname, node, prop, '-t', 'bx']
if default is not None:
args += ['-d', str(default)]
if typespec is not None:
args += ['-t%s' % typespec]
out = command.Output('fdtget', *args)
return out.strip()

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#!/usr/bin/python
#
# Copyright (C) 2016 Google, Inc
# Written by Simon Glass <sjg@chromium.org>
#
# SPDX-License-Identifier: GPL-2.0+
#
import struct
# A list of types we support
(TYPE_BYTE, TYPE_INT, TYPE_STRING, TYPE_BOOL) = range(4)
def BytesToValue(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(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 fdt32_to_cpu(val):
"""Convert a device tree cell to an integer
Args:
Value to convert (4-character string representing the cell value)
Return:
A native-endian integer value
"""
return struct.unpack(">I", val)[0]