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/README

@@ -278,9 +278,12 @@ offset:
 
 align:
 	This sets the alignment of the entry. The entry offset is adjusted
-	so that the entry starts on an aligned boundary within the image. For
-	example 'align = <16>' means that the entry will start on a 16-byte
-	boundary. Alignment shold be a power of 2. If 'align' is not
+	so that the entry starts on an aligned boundary within the containing
+	section or image. For example 'align = <16>' means that the entry will
+	start on a 16-byte boundary. This may mean that padding is added before
+	the entry. The padding is part of the containing section but is not
+	included in the entry, meaning that an empty space may be created before
+	the entry starts. Alignment should be a power of 2. If 'align' is not
 	provided, no alignment is performed.
 
 size:
@@ -308,14 +311,22 @@ pad-after:
 align-size:
 	This sets the alignment of the entry size. For example, to ensure
 	that the size of an entry is a multiple of 64 bytes, set this to 64.
-	If 'align-size' is not provided, no alignment is performed.
+	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 is that the entry ends with the padding
+	bytes, so may grow. If 'align-size' is not provided, no alignment is
+	performed.
 
 align-end:
-	This sets the alignment of the end of an entry. Some entries require
-	that they end on an alignment boundary, regardless of where they
-	start. This does not move the start of the entry, so the contents of
-	the entry will still start at the beginning. But there may be padding
-	at the end. If 'align-end' is not provided, no alignment is performed.
+	This sets the alignment of the end of an entry with respect to the
+	containing section. Some entries require that they end on an alignment
+	boundary, regardless of where they start. This does not move the start
+	of the entry, so the contents of the entry will still start at the
+	beginning. But there may be padding at the end. 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
+	is that the entry ends with the padding bytes, so may grow.
+	If 'align-end' is not provided, no alignment is performed.
 
 filename:
 	For 'blob' types this provides the filename containing the binary to

tools/binman/entry.py

@@ -48,9 +48,11 @@ class Entry(object):
         uncomp_size: Size of uncompressed data in bytes, if the entry is
             compressed, else None
         contents_size: Size of contents in bytes, 0 by default
-        align: Entry start offset alignment, or None
+        align: Entry start offset alignment relative to the start of the
+            containing section, or None
         align_size: Entry size alignment, or None
-        align_end: Entry end offset alignment, or None
+        align_end: Entry end offset alignment relative to the start of the
+            containing section, or None
         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.

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: