binman: Add an image header

It is useful to be able to quickly locate the FDT map in the image. An
easy way to do this is with a pointer at the start or end of the image.

Add an 'image header' entry, which places a magic number followed by a
pointer to the FDT map. This can be located at the start or end of the
image, or at a chosen location.

As part of this, update GetSiblingImagePos() to detect missing siblings.

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

1 files changed, 19 insertions, 0 deletions

diff --git a/tools/binman/README.entries b/tools/binman/README.entries
index 7014d36f5f..598d8278a7 100644
--- a/tools/binman/README.entries
+++ b/tools/binman/README.entries
@@ -331,6 +331,25 @@ README.chromium for how to obtain the required keys and tools.
 
 
 
+Entry: image-header: An entry which contains a pointer to the FDT map
+---------------------------------------------------------------------
+
+Properties / Entry arguments:
+    location: Location of header ("start" or "end" of image). This is
+        optional. If omitted then the entry must have an offset property.
+
+This adds an 8-byte entry to the start or end of the image, pointing to the
+location of the FDT map. The format is a magic number followed by an offset
+from the start or end of the image, in twos-compliment format.
+
+This entry must be in the top-level part of the image.
+
+NOTE: If the location is at the start/end, you will probably need to specify
+sort-by-offset for the image, unless you actually put the image header
+first/last in the entry list.
+
+
+
 Entry: intel-cmc: Entry containing an Intel Chipset Micro Code (CMC) file
 -------------------------------------------------------------------------