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 ---
Changes in v3: - Update comments a little - Add GetEmpty() to obtain an empty/zero value of a given type
Changes in v2: None
tools/dtoc/.gitignore | 1 + tools/dtoc/fdt_fallback.py | 207 +++++++++++++++++++++++++++++++++++++++++++++ tools/dtoc/fdt_util.py | 86 +++++++++++++++++++ 3 files changed, 294 insertions(+) create mode 100644 tools/dtoc/.gitignore create mode 100644 tools/dtoc/fdt_fallback.py create mode 100644 tools/dtoc/fdt_util.py
diff --git a/tools/dtoc/.gitignore b/tools/dtoc/.gitignore new file mode 100644 index 0000000..0d20b64 --- /dev/null +++ b/tools/dtoc/.gitignore @@ -0,0 +1 @@ +*.pyc diff --git a/tools/dtoc/fdt_fallback.py b/tools/dtoc/fdt_fallback.py new file mode 100644 index 0000000..14decf3 --- /dev/null +++ b/tools/dtoc/fdt_fallback.py @@ -0,0 +1,207 @@ +#!/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() diff --git a/tools/dtoc/fdt_util.py b/tools/dtoc/fdt_util.py new file mode 100644 index 0000000..929b524 --- /dev/null +++ b/tools/dtoc/fdt_util.py @@ -0,0 +1,86 @@ +#!/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]