binman: Allow external binaries to be missing

Sometimes it is useful to build an image even though external binaries are
not present. This allows the build system to continue to function without
these files, albeit not producing valid images.

U-Boot does with with ATF (ARM Trusted Firmware) today.

Add a new flag to binman to request this behaviour.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

tools/binman/control.py

@@ -387,7 +387,7 @@ def PrepareImagesAndDtbs(dtb_fname, select_images, update_fdt):
 
 
 def ProcessImage(image, update_fdt, write_map, get_contents=True,
-                 allow_resize=True):
+                 allow_resize=True, allow_missing=False):
     """Perform all steps for this image, including checking and # writing it.
 
     This means that errors found with a later image will be reported after
@@ -402,8 +402,10 @@ def ProcessImage(image, update_fdt, write_map, get_contents=True,
             the contents is already present
         allow_resize: True to allow entries to change size (this does a re-pack
             of the entries), False to raise an exception
+        allow_missing: Allow blob_ext objects to be missing
     """
     if get_contents:
+        image.SetAllowMissing(allow_missing)
         image.GetEntryContents()
     image.GetEntryOffsets()
 
@@ -523,7 +525,8 @@ def Binman(args):
             images = PrepareImagesAndDtbs(dtb_fname, args.image,
                                           args.update_fdt)
             for image in images.values():
-                ProcessImage(image, args.update_fdt, args.map)
+                ProcessImage(image, args.update_fdt, args.map,
+                             allow_missing=args.allow_missing)
 
             # Write the updated FDTs to our output files
             for dtb_item in state.GetAllFdts():