411 lines
12 KiB
Python
411 lines
12 KiB
Python
#!/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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import sys
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import fdt_util
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import libfdt
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# This deals with a device tree, presenting it as an assortment of Node and
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# Prop objects, representing nodes and properties, respectively. This file
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# contains the base classes and defines the high-level API. You can use
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# FdtScan() as a convenience function to create and scan an Fdt.
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# This implementation uses a libfdt Python library to access the device tree,
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# so it is fairly efficient.
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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 CheckErr(errnum, msg):
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if errnum:
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raise ValueError('Error %d: %s: %s' %
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(errnum, libfdt.fdt_strerror(errnum), msg))
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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, node, offset, name, bytes):
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self._node = node
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self._offset = offset
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self.name = name
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self.value = None
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self.bytes = str(bytes)
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if not bytes:
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self.type = TYPE_BOOL
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self.value = True
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return
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self.type, self.value = self.BytesToValue(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 = [self.value]
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if type(self.value) == list and len(newprop.value) > len(self.value):
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val = self.GetEmpty(self.type)
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while len(self.value) < len(newprop.value):
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self.value.append(val)
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def BytesToValue(self, 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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bytes = str(bytes)
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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(self, 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 GetOffset(self):
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"""Get the offset of a property
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Returns:
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The offset of the property (struct fdt_property) within the file
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"""
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return self._node._fdt.GetStructOffset(self._offset)
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class Node:
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"""A device tree node
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Properties:
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offset: Integer offset in the device tree
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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, parent, offset, name, path):
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self._fdt = fdt
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self.parent = parent
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self._offset = offset
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self.name = name
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self.path = path
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self.subnodes = []
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self.props = {}
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def _FindNode(self, name):
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"""Find a node given its name
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Args:
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name: Node name to look for
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Returns:
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Node object if found, else None
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"""
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for subnode in self.subnodes:
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if subnode.name == name:
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return subnode
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return None
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def Offset(self):
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"""Returns the offset of a node, after checking the cache
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This should be used instead of self._offset directly, to ensure that
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the cache does not contain invalid offsets.
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"""
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self._fdt.CheckCache()
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return self._offset
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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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self.props = self._fdt.GetProps(self)
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offset = libfdt.fdt_first_subnode(self._fdt.GetFdt(), self.Offset())
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while offset >= 0:
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sep = '' if self.path[-1] == '/' else '/'
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name = self._fdt._fdt_obj.get_name(offset)
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path = self.path + sep + name
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node = Node(self._fdt, self, offset, name, path)
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self.subnodes.append(node)
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node.Scan()
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offset = libfdt.fdt_next_subnode(self._fdt.GetFdt(), offset)
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def Refresh(self, my_offset):
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"""Fix up the _offset for each node, recursively
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Note: This does not take account of property offsets - these will not
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be updated.
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"""
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if self._offset != my_offset:
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#print '%s: %d -> %d\n' % (self.path, self._offset, my_offset)
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self._offset = my_offset
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offset = libfdt.fdt_first_subnode(self._fdt.GetFdt(), self._offset)
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for subnode in self.subnodes:
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subnode.Refresh(offset)
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offset = libfdt.fdt_next_subnode(self._fdt.GetFdt(), offset)
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def DeleteProp(self, prop_name):
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"""Delete a property of a node
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The property is deleted and the offset cache is invalidated.
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Args:
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prop_name: Name of the property to delete
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Raises:
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ValueError if the property does not exist
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"""
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CheckErr(libfdt.fdt_delprop(self._fdt.GetFdt(), self.Offset(), prop_name),
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"Node '%s': delete property: '%s'" % (self.path, prop_name))
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del self.props[prop_name]
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self._fdt.Invalidate()
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class Fdt:
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"""Provides simple access to a flat device tree blob using libfdts.
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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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self._cached_offsets = False
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if self._fname:
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self._fname = fdt_util.EnsureCompiled(self._fname)
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with open(self._fname) as fd:
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self._fdt = bytearray(fd.read())
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self._fdt_obj = libfdt.Fdt(self._fdt)
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def Scan(self, root='/'):
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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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Args:
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root: Ignored
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TODO(sjg@chromium.org): Implement the 'root' parameter
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"""
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self._root = self.Node(self, None, 0, '/', '/')
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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 GetNode(self, path):
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"""Look up a node from its path
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Args:
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path: Path to look up, e.g. '/microcode/update@0'
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Returns:
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Node object, or None if not found
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"""
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node = self._root
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for part in path.split('/')[1:]:
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node = node._FindNode(part)
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if not node:
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return None
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return node
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def Flush(self):
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"""Flush device tree changes back to the file
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If the device tree has changed in memory, write it back to the file.
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"""
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with open(self._fname, 'wb') as fd:
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fd.write(self._fdt)
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def Pack(self):
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"""Pack the device tree down to its minimum size
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When nodes and properties shrink or are deleted, wasted space can
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build up in the device tree binary.
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"""
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CheckErr(libfdt.fdt_pack(self._fdt), 'pack')
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fdt_len = libfdt.fdt_totalsize(self._fdt)
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del self._fdt[fdt_len:]
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def GetFdt(self):
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"""Get the contents of the FDT
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Returns:
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The FDT contents as a string of bytes
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"""
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return self._fdt
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def CheckErr(errnum, msg):
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if errnum:
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raise ValueError('Error %d: %s: %s' %
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(errnum, libfdt.fdt_strerror(errnum), msg))
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def GetProps(self, node):
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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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Returns:
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A dictionary containing all the properties, indexed by node name.
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The entries are Prop objects.
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Raises:
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ValueError: if the node does not exist.
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"""
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props_dict = {}
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poffset = libfdt.fdt_first_property_offset(self._fdt, node._offset)
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while poffset >= 0:
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p = self._fdt_obj.get_property_by_offset(poffset)
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prop = Prop(node, poffset, p.name, p.value)
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props_dict[prop.name] = prop
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poffset = libfdt.fdt_next_property_offset(self._fdt, poffset)
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return props_dict
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def Invalidate(self):
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"""Mark our offset cache as invalid"""
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self._cached_offsets = False
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def CheckCache(self):
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"""Refresh the offset cache if needed"""
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if self._cached_offsets:
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return
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self.Refresh()
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self._cached_offsets = True
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def Refresh(self):
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"""Refresh the offset cache"""
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self._root.Refresh(0)
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def GetStructOffset(self, offset):
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"""Get the file offset of a given struct offset
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Args:
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offset: Offset within the 'struct' region of the device tree
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Returns:
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Position of @offset within the device tree binary
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"""
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return libfdt.fdt_off_dt_struct(self._fdt) + offset
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@classmethod
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def Node(self, fdt, parent, offset, name, path):
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"""Create a new node
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This is used by Fdt.Scan() to create a new node using the correct
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class.
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Args:
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fdt: Fdt object
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parent: Parent node, or None if this is the root node
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offset: Offset of node
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name: Node name
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path: Full path to node
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"""
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node = Node(fdt, parent, offset, name, path)
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return node
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def FdtScan(fname):
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"""Returns a new Fdt object from the implementation we are using"""
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dtb = Fdt(fname)
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dtb.Scan()
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return dtb
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