2 # SPDX-License-Identifier: GPL-2.0+
4 # Copyright (C) 2016 Google, Inc
5 # Written by Simon Glass <sjg@chromium.org>
14 # This deals with a device tree, presenting it as an assortment of Node and
15 # Prop objects, representing nodes and properties, respectively. This file
16 # contains the base classes and defines the high-level API. You can use
17 # FdtScan() as a convenience function to create and scan an Fdt.
19 # This implementation uses a libfdt Python library to access the device tree,
20 # so it is fairly efficient.
22 # A list of types we support
23 (TYPE_BYTE, TYPE_INT, TYPE_STRING, TYPE_BOOL, TYPE_INT64) = range(5)
25 def CheckErr(errnum, msg):
27 raise ValueError('Error %d: %s: %s' %
28 (errnum, libfdt.fdt_strerror(errnum), msg))
31 """A device tree property
34 name: Property name (as per the device tree)
35 value: Property value as a string of bytes, or a list of strings of
39 def __init__(self, node, offset, name, bytes):
44 self.bytes = str(bytes)
49 self.type, self.value = self.BytesToValue(bytes)
52 """Get a (single) phandle value from a property
54 Gets the phandle valuie from a property and returns it as an integer
56 return fdt_util.fdt32_to_cpu(self.value[:4])
58 def Widen(self, newprop):
59 """Figure out which property type is more general
61 Given a current property and a new property, this function returns the
62 one that is less specific as to type. The less specific property will
63 be ble to represent the data in the more specific property. This is
75 He we want to use an int array for 'value'. The first property
76 suggests that a single int is enough, but the second one shows that
77 it is not. Calling this function with these two propertes would
78 update the current property to be like the second, since it is less
81 if newprop.type < self.type:
82 self.type = newprop.type
84 if type(newprop.value) == list and type(self.value) != list:
85 self.value = [self.value]
87 if type(self.value) == list and len(newprop.value) > len(self.value):
88 val = self.GetEmpty(self.type)
89 while len(self.value) < len(newprop.value):
90 self.value.append(val)
92 def BytesToValue(self, bytes):
93 """Converts a string of bytes into a type and value
96 A string containing bytes
101 Data, either a single element or a list of elements. Each element
103 TYPE_STRING: string value from the property
104 TYPE_INT: a byte-swapped integer stored as a 4-byte string
105 TYPE_BYTE: a byte stored as a single-byte string
109 strings = bytes.split('\0')
111 count = len(strings) - 1
112 if count > 0 and not strings[-1]:
113 for string in strings[:-1]:
118 if ch < ' ' or ch > '~':
125 return TYPE_STRING, strings[0]
127 return TYPE_STRING, strings[:-1]
130 return TYPE_BYTE, bytes[0]
132 return TYPE_BYTE, list(bytes)
134 for i in range(0, size, 4):
135 val.append(bytes[i:i + 4])
137 return TYPE_INT, val[0]
142 def GetEmpty(self, type):
143 """Get an empty / zero value of the given type
146 A single value of the given type
148 if type == TYPE_BYTE:
150 elif type == TYPE_INT:
151 return struct.pack('<I', 0);
152 elif type == TYPE_STRING:
158 """Get the offset of a property
161 The offset of the property (struct fdt_property) within the file
163 return self._node._fdt.GetStructOffset(self._offset)
166 """A device tree node
169 offset: Integer offset in the device tree
170 name: Device tree node tname
171 path: Full path to node, along with the node name itself
172 _fdt: Device tree object
173 subnodes: A list of subnodes for this node, each a Node object
174 props: A dict of properties for this node, each a Prop object.
175 Keyed by property name
177 def __init__(self, fdt, parent, offset, name, path):
180 self._offset = offset
186 def _FindNode(self, name):
187 """Find a node given its name
190 name: Node name to look for
192 Node object if found, else None
194 for subnode in self.subnodes:
195 if subnode.name == name:
200 """Returns the offset of a node, after checking the cache
202 This should be used instead of self._offset directly, to ensure that
203 the cache does not contain invalid offsets.
205 self._fdt.CheckCache()
209 """Scan a node's properties and subnodes
211 This fills in the props and subnodes properties, recursively
212 searching into subnodes so that the entire tree is built.
214 self.props = self._fdt.GetProps(self)
215 phandle = self.props.get('phandle')
217 val = fdt_util.fdt32_to_cpu(phandle.value)
218 self._fdt.phandle_to_node[val] = self
220 offset = libfdt.fdt_first_subnode(self._fdt.GetFdt(), self.Offset())
222 sep = '' if self.path[-1] == '/' else '/'
223 name = self._fdt._fdt_obj.get_name(offset)
224 path = self.path + sep + name
225 node = Node(self._fdt, self, offset, name, path)
226 self.subnodes.append(node)
229 offset = libfdt.fdt_next_subnode(self._fdt.GetFdt(), offset)
231 def Refresh(self, my_offset):
232 """Fix up the _offset for each node, recursively
234 Note: This does not take account of property offsets - these will not
237 if self._offset != my_offset:
238 self._offset = my_offset
239 offset = libfdt.fdt_first_subnode(self._fdt.GetFdt(), self._offset)
240 for subnode in self.subnodes:
241 subnode.Refresh(offset)
242 offset = libfdt.fdt_next_subnode(self._fdt.GetFdt(), offset)
244 def DeleteProp(self, prop_name):
245 """Delete a property of a node
247 The property is deleted and the offset cache is invalidated.
250 prop_name: Name of the property to delete
252 ValueError if the property does not exist
254 CheckErr(libfdt.fdt_delprop(self._fdt.GetFdt(), self.Offset(), prop_name),
255 "Node '%s': delete property: '%s'" % (self.path, prop_name))
256 del self.props[prop_name]
257 self._fdt.Invalidate()
260 """Provides simple access to a flat device tree blob using libfdts.
263 fname: Filename of fdt
264 _root: Root of device tree (a Node object)
266 def __init__(self, fname):
268 self._cached_offsets = False
269 self.phandle_to_node = {}
271 self._fname = fdt_util.EnsureCompiled(self._fname)
273 with open(self._fname) as fd:
274 self._fdt = bytearray(fd.read())
275 self._fdt_obj = libfdt.Fdt(self._fdt)
277 def Scan(self, root='/'):
278 """Scan a device tree, building up a tree of Node objects
280 This fills in the self._root property
285 TODO(sjg@chromium.org): Implement the 'root' parameter
287 self._root = self.Node(self, None, 0, '/', '/')
291 """Get the root Node of the device tree
298 def GetNode(self, path):
299 """Look up a node from its path
302 path: Path to look up, e.g. '/microcode/update@0'
304 Node object, or None if not found
307 for part in path.split('/')[1:]:
308 node = node._FindNode(part)
314 """Flush device tree changes back to the file
316 If the device tree has changed in memory, write it back to the file.
318 with open(self._fname, 'wb') as fd:
322 """Pack the device tree down to its minimum size
324 When nodes and properties shrink or are deleted, wasted space can
325 build up in the device tree binary.
327 CheckErr(libfdt.fdt_pack(self._fdt), 'pack')
328 fdt_len = libfdt.fdt_totalsize(self._fdt)
329 del self._fdt[fdt_len:]
332 """Get the contents of the FDT
335 The FDT contents as a string of bytes
340 """Get the contents of the FDT
343 The FDT contents as a libfdt.Fdt object
347 def CheckErr(self, errnum, msg):
349 raise ValueError('Error %d: %s: %s' %
350 (errnum, libfdt.fdt_strerror(errnum), msg))
352 def GetProps(self, node):
353 """Get all properties from a node.
356 node: Full path to node name to look in.
359 A dictionary containing all the properties, indexed by node name.
360 The entries are Prop objects.
363 ValueError: if the node does not exist.
366 poffset = libfdt.fdt_first_property_offset(self._fdt, node._offset)
368 p = self._fdt_obj.get_property_by_offset(poffset)
369 prop = Prop(node, poffset, p.name, p)
370 props_dict[prop.name] = prop
372 poffset = libfdt.fdt_next_property_offset(self._fdt, poffset)
375 def Invalidate(self):
376 """Mark our offset cache as invalid"""
377 self._cached_offsets = False
379 def CheckCache(self):
380 """Refresh the offset cache if needed"""
381 if self._cached_offsets:
384 self._cached_offsets = True
387 """Refresh the offset cache"""
388 self._root.Refresh(0)
390 def GetStructOffset(self, offset):
391 """Get the file offset of a given struct offset
394 offset: Offset within the 'struct' region of the device tree
396 Position of @offset within the device tree binary
398 return libfdt.fdt_off_dt_struct(self._fdt) + offset
401 def Node(self, fdt, parent, offset, name, path):
404 This is used by Fdt.Scan() to create a new node using the correct
409 parent: Parent node, or None if this is the root node
410 offset: Offset of node
412 path: Full path to node
414 node = Node(fdt, parent, offset, name, path)
418 """Returns a new Fdt object from the implementation we are using"""