dtoc: Move the fdt library selection into fdt_select

Rather than have dtc worry about which fdt library to use, move this into
a helper file. Add a function which creates a new Fdt object and scans it,
regardless of the implementation.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/dtoc/dtoc.py

@@ -12,23 +12,12 @@ import os
 import struct
 import sys
 
-import fdt_util
-
 # Bring in the patman libraries
 our_path = os.path.dirname(os.path.realpath(__file__))
 sys.path.append(os.path.join(our_path, '../patman'))
 
-# Bring in either the normal fdt library (which relies on libfdt) or the
-# fallback one (which uses fdtget and is slower). Both provide the same
-# interfface for this file to use.
-try:
-    from fdt import Fdt
-    import fdt
-    have_libfdt = True
-except ImportError:
-    have_libfdt = False
-    from fdt_fallback import Fdt
-    import fdt_fallback as fdt
+import fdt_select
+import fdt_util
 
 # When we see these properties we ignore them - i.e. do not create a structure member
 PROP_IGNORE_LIST = [
@@ -177,8 +166,7 @@ class DtbPlatdata:
         Once this is done, self.fdt.GetRoot() can be called to obtain the
         device tree root node, and progress from there.
         """
-        self.fdt = Fdt(self._dtb_fname)
-        self.fdt.Scan()
+        self.fdt = fdt_select.FdtScan(self._dtb_fname)
 
     def ScanTree(self):
         """Scan the device tree for useful information

tools/dtoc/fdt_select.py

@@ -0,0 +1,23 @@
+#!/usr/bin/python
+#
+# Copyright (C) 2016 Google, Inc
+# Written by Simon Glass <sjg@chromium.org>
+#
+# SPDX-License-Identifier:      GPL-2.0+
+#
+
+# Bring in either the normal fdt library (which relies on libfdt) or the
+# fallback one (which uses fdtget and is slower). Both provide the same
+# interface for this file to use.
+try:
+    import fdt
+    have_libfdt = True
+except ImportError:
+    have_libfdt = False
+    import fdt_fallback as fdt
+
+def FdtScan(fname):
+    """Returns a new Fdt object from the implementation we are using"""
+    dtb = fdt.Fdt(fname)
+    dtb.Scan()
+    return dtb