binman: Expand docs and test for alignment

Alignment does form 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/ftest.py

@@ -785,7 +785,8 @@ class TestFunctional(unittest.TestCase):
 
     def testPackExtra(self):
         """Test that extra packing feature works as expected"""
-        data = self._DoReadFile('009_pack_extra.dts')
+        data, _, _, out_dtb_fname = self._DoReadFileDtb('009_pack_extra.dts',
+                                                        update_dtb=True)
 
         self.assertIn('image', control.images)
         image = control.images['image']
@@ -844,6 +845,36 @@ class TestFunctional(unittest.TestCase):
         self.CheckNoGaps(entries)
         self.assertEqual(128, image.size)
 
+        dtb = fdt.Fdt(out_dtb_fname)
+        dtb.Scan()
+        props = self._GetPropTree(dtb, ['size', 'offset', 'image-pos'])
+        expected = {
+            'image-pos': 0,
+            'offset': 0,
+            'size': 128,
+
+            'u-boot:image-pos': 0,
+            'u-boot:offset': 0,
+            'u-boot:size': 3 + 5 + len(U_BOOT_DATA),
+
+            'u-boot-align-size-nop:image-pos': 12,
+            'u-boot-align-size-nop:offset': 12,
+            'u-boot-align-size-nop:size': 4,
+
+            'u-boot-align-size:image-pos': 16,
+            'u-boot-align-size:offset': 16,
+            'u-boot-align-size:size': 32,
+
+            'u-boot-align-end:image-pos': 48,
+            'u-boot-align-end:offset': 48,
+            'u-boot-align-end:size': 16,
+
+            'u-boot-align-both:image-pos': 64,
+            'u-boot-align-both:offset': 64,
+            'u-boot-align-both:size': 64,
+            }
+        self.assertEqual(expected, props)
+
     def testPackAlignPowerOf2(self):
         """Test that invalid entry alignment is detected"""
         with self.assertRaises(ValueError) as e: