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/patman/tools.py

@@ -114,14 +114,16 @@ def SetInputDirs(dirname):
     indir = dirname
     tout.Debug("Using input directories %s" % indir)
 
-def GetInputFilename(fname):
+def GetInputFilename(fname, allow_missing=False):
     """Return a filename for use as input.
 
     Args:
         fname: Filename to use for new file
+        allow_missing: True if the filename can be missing
 
     Returns:
-        The full path of the filename, within the input directory
+        The full path of the filename, within the input directory, or
+        None on error
     """
     if not indir or fname[:1] == '/':
         return fname
@@ -130,6 +132,8 @@ def GetInputFilename(fname):
         if os.path.exists(pathname):
             return pathname
 
+    if allow_missing:
+        return None
     raise ValueError("Filename '%s' not found in input path (%s) (cwd='%s')" %
                      (fname, ','.join(indir), os.getcwd()))