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>

tools/dtoc/.gitignore

+*.pyc

tools/dtoc/fdt_fallback.py

+#!/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()

tools/dtoc/fdt_util.py

+#!/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]