dm: Add a library to provide simple device-tree access
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>
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Simon Glass
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*.pyc
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#!/usr/bin/python
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#
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# Copyright (C) 2016 Google, Inc
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# Written by Simon Glass <sjg@chromium.org>
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#
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# SPDX-License-Identifier: GPL-2.0+
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#
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import command
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import fdt_util
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import sys
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# This deals with a device tree, presenting it as a list of Node and Prop
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# objects, representing nodes and properties, respectively.
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#
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# This implementation uses the fdtget tool to access the device tree, so it
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# is not very efficient for larger trees. The tool is called once for each
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# node and property in the tree.
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class Prop:
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"""A device tree property
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Properties:
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name: Property name (as per the device tree)
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value: Property value as a string of bytes, or a list of strings of
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bytes
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type: Value type
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"""
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def __init__(self, name, byte_list_str):
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self.name = name
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self.value = None
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if not byte_list_str.strip():
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self.type = fdt_util.TYPE_BOOL
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return
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bytes = [chr(int(byte, 16)) for byte in byte_list_str.strip().split(' ')]
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self.type, self.value = fdt_util.BytesToValue(''.join(bytes))
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def GetPhandle(self):
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"""Get a (single) phandle value from a property
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Gets the phandle valuie from a property and returns it as an integer
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"""
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return fdt_util.fdt32_to_cpu(self.value[:4])
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def Widen(self, newprop):
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"""Figure out which property type is more general
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Given a current property and a new property, this function returns the
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one that is less specific as to type. The less specific property will
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be ble to represent the data in the more specific property. This is
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used for things like:
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node1 {
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compatible = "fred";
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value = <1>;
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};
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node1 {
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compatible = "fred";
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value = <1 2>;
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};
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He we want to use an int array for 'value'. The first property
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suggests that a single int is enough, but the second one shows that
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it is not. Calling this function with these two propertes would
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update the current property to be like the second, since it is less
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specific.
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"""
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if newprop.type < self.type:
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self.type = newprop.type
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if type(newprop.value) == list and type(self.value) != list:
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self.value = newprop.value
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class Node:
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"""A device tree node
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Properties:
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name: Device tree node tname
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path: Full path to node, along with the node name itself
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_fdt: Device tree object
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subnodes: A list of subnodes for this node, each a Node object
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props: A dict of properties for this node, each a Prop object.
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Keyed by property name
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"""
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def __init__(self, fdt, name, path):
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self.name = name
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self.path = path
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self._fdt = fdt
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self.subnodes = []
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self.props = {}
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def Scan(self):
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"""Scan a node's properties and subnodes
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This fills in the props and subnodes properties, recursively
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searching into subnodes so that the entire tree is built.
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"""
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for name, byte_list_str in self._fdt.GetProps(self.path).iteritems():
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prop = Prop(name, byte_list_str)
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self.props[name] = prop
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for name in self._fdt.GetSubNodes(self.path):
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sep = '' if self.path[-1] == '/' else '/'
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path = self.path + sep + name
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node = Node(self._fdt, name, path)
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self.subnodes.append(node)
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node.Scan()
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class Fdt:
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"""Provides simple access to a flat device tree blob.
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Properties:
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fname: Filename of fdt
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_root: Root of device tree (a Node object)
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"""
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def __init__(self, fname):
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self.fname = fname
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def Scan(self):
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"""Scan a device tree, building up a tree of Node objects
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This fills in the self._root property
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"""
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self._root = Node(self, '/', '/')
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self._root.Scan()
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def GetRoot(self):
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"""Get the root Node of the device tree
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Returns:
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The root Node object
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"""
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return self._root
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def GetSubNodes(self, node):
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"""Returns a list of sub-nodes of a given node
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Args:
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node: Node name to return children from
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Returns:
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List of children in the node (each a string node name)
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Raises:
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CmdError: if the node does not exist.
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"""
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out = command.Output('fdtget', self.fname, '-l', node)
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return out.strip().splitlines()
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def GetProps(self, node, convert_dashes=False):
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"""Get all properties from a node
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Args:
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node: full path to node name to look in
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convert_dashes: True to convert - to _ in node names
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Returns:
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A dictionary containing all the properties, indexed by node name.
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The entries are simply strings - no decoding of lists or numbers
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is done.
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Raises:
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CmdError: if the node does not exist.
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"""
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out = command.Output('fdtget', self.fname, node, '-p')
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props = out.strip().splitlines()
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props_dict = {}
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for prop in props:
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name = prop
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if convert_dashes:
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prop = re.sub('-', '_', prop)
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props_dict[prop] = self.GetProp(node, name)
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return props_dict
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def GetProp(self, node, prop, default=None, typespec=None):
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"""Get a property from a device tree.
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This looks up the given node and property, and returns the value as a
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string,
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If the node or property does not exist, this will return the default
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value.
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Args:
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node: Full path to node to look up.
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prop: Property name to look up.
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default: Default value to return if nothing is present in the fdt,
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or None to raise in this case. This will be converted to a
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string.
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typespec: Type character to use (None for default, 's' for string)
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Returns:
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string containing the property value.
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Raises:
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CmdError: if the property does not exist and no default is provided.
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"""
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args = [self.fname, node, prop, '-t', 'bx']
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if default is not None:
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args += ['-d', str(default)]
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if typespec is not None:
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args += ['-t%s' % typespec]
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out = command.Output('fdtget', *args)
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return out.strip()
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@ -0,0 +1,86 @@
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#!/usr/bin/python
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#
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# Copyright (C) 2016 Google, Inc
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# Written by Simon Glass <sjg@chromium.org>
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#
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# SPDX-License-Identifier: GPL-2.0+
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#
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import struct
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# A list of types we support
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(TYPE_BYTE, TYPE_INT, TYPE_STRING, TYPE_BOOL) = range(4)
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def BytesToValue(bytes):
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"""Converts a string of bytes into a type and value
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Args:
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A string containing bytes
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Return:
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A tuple:
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Type of data
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Data, either a single element or a list of elements. Each element
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is one of:
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TYPE_STRING: string value from the property
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TYPE_INT: a byte-swapped integer stored as a 4-byte string
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TYPE_BYTE: a byte stored as a single-byte string
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"""
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size = len(bytes)
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strings = bytes.split('\0')
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is_string = True
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count = len(strings) - 1
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if count > 0 and not strings[-1]:
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for string in strings[:-1]:
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if not string:
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is_string = False
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break
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for ch in string:
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if ch < ' ' or ch > '~':
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is_string = False
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break
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else:
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is_string = False
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if is_string:
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if count == 1:
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return TYPE_STRING, strings[0]
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else:
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return TYPE_STRING, strings[:-1]
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if size % 4:
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if size == 1:
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return TYPE_BYTE, bytes[0]
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else:
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return TYPE_BYTE, list(bytes)
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val = []
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for i in range(0, size, 4):
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val.append(bytes[i:i + 4])
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if size == 4:
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return TYPE_INT, val[0]
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else:
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return TYPE_INT, val
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def GetEmpty(type):
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"""Get an empty / zero value of the given type
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Returns:
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A single value of the given type
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"""
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if type == TYPE_BYTE:
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return chr(0)
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elif type == TYPE_INT:
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return struct.pack('<I', 0);
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elif type == TYPE_STRING:
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return ''
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else:
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return True
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def fdt32_to_cpu(val):
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"""Convert a device tree cell to an integer
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Args:
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Value to convert (4-character string representing the cell value)
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Return:
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A native-endian integer value
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"""
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return struct.unpack(">I", val)[0]
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