binman: Expand docs and test for padding

Padding becomes part of the entry once the image is written out, but
within binman the entry contents does not include the padding. Add
documentation to make this clear, as well as a test.

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

tools/binman/README

@@ -290,14 +290,20 @@ size:
 
 pad-before:
 	Padding before the contents of the entry. Normally this is 0, meaning
-	that the contents start at the beginning of the entry. This can be
-	offset the entry contents a little. Defaults to 0.
+	that the contents start at the beginning of the entry. This can be used
+	to offset the entry contents a little. While this does not affect the
+	contents of the entry within binman itself (the padding is performed
+	only when its parent section is assembled), the end result will be that
+	the entry starts with the padding bytes, so may grow. Defaults to 0.
 
 pad-after:
 	Padding after the contents of the entry. Normally this is 0, meaning
 	that the entry ends at the last byte of content (unless adjusted by
 	other properties). This allows room to be created in the image for
-	this entry to expand later. Defaults to 0.
+	this entry to expand later. While this does not affect the contents of
+	the entry within binman itself (the padding is performed only when its
+	parent section is assembled), the end result will be that the entry ends
+	with the padding bytes, so may grow. Defaults to 0.
 
 align-size:
 	This sets the alignment of the entry size. For example, to ensure

tools/binman/entry.py

@@ -51,9 +51,14 @@ class Entry(object):
         align: Entry start offset alignment, or None
         align_size: Entry size alignment, or None
         align_end: Entry end offset alignment, or None
-        pad_before: Number of pad bytes before the contents, 0 if none
-        pad_after: Number of pad bytes after the contents, 0 if none
-        data: Contents of entry (string of bytes)
+        pad_before: Number of pad bytes before the contents when it is placed
+            in the containing section, 0 if none. The pad bytes become part of
+            the entry.
+        pad_after: Number of pad bytes after the contents when it is placed in
+            the containing section, 0 if none. The pad bytes become part of
+            the entry.
+        data: Contents of entry (string of bytes). This does not include
+            padding created by pad_before or pad_after
         compress: Compression algoithm used (e.g. 'lz4'), 'none' if none
         orig_offset: Original offset value read from node
         orig_size: Original size value read from node

tools/binman/ftest.py

@@ -3548,12 +3548,39 @@ class TestFunctional(unittest.TestCase):
 
     def testPadInSections(self):
         """Test pad-before, pad-after for entries in sections"""
-        data = self._DoReadFile('166_pad_in_sections.dts')
+        data, _, _, out_dtb_fname = self._DoReadFileDtb(
+            '166_pad_in_sections.dts', update_dtb=True)
         expected = (U_BOOT_DATA + tools.GetBytes(ord('!'), 12) +
                     U_BOOT_DATA + tools.GetBytes(ord('!'), 6) +
                     U_BOOT_DATA)
         self.assertEqual(expected, data)
 
+        dtb = fdt.Fdt(out_dtb_fname)
+        dtb.Scan()
+        props = self._GetPropTree(dtb, ['size', 'image-pos', 'offset'])
+        expected = {
+            'image-pos': 0,
+            'offset': 0,
+            'size': 12 + 6 + 3 * len(U_BOOT_DATA),
+
+            'section:image-pos': 0,
+            'section:offset': 0,
+            'section:size': 12 + 6 + 3 * len(U_BOOT_DATA),
+
+            'section/before:image-pos': 0,
+            'section/before:offset': 0,
+            'section/before:size': len(U_BOOT_DATA),
+
+            'section/u-boot:image-pos': 4,
+            'section/u-boot:offset': 4,
+            'section/u-boot:size': 12 + len(U_BOOT_DATA) + 6,
+
+            'section/after:image-pos': 26,
+            'section/after:offset': 26,
+            'section/after:size': len(U_BOOT_DATA),
+            }
+        self.assertEqual(expected, props)
+
     def testFitImageSubentryAlignment(self):
         """Test relative alignability of FIT image subentries"""
         entry_args = {