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/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]