binman: Don't assume there is an ME region

At present having a descriptor means that there is an ME (Intel
Management Engine) entry as well. The descriptor provides the ME location
and assumes that it is present.

For some SoCs this is not true. Before providing the location of a
potentially non-existent entry, check if it is present.

Update the comment in the ME entry also.

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

tools/binman/README.entries

@@ -206,6 +206,8 @@ does not directly execute code in the ME binary.
 
 A typical filename is 'me.bin'.
 
+The position of this entry is generally set by the intel-descriptor entry.
+
 See README.x86 for information about x86 binary blobs.
 
 

tools/binman/entry.py

@@ -544,3 +544,12 @@ features to produce new behaviours.
             # the data grows. This should not fail, but check it to be sure.
             if not self.ObtainContents():
                 self.Raise('Cannot obtain contents when expanding entry')
+
+    def HasSibling(self, name):
+        """Check if there is a sibling of a given name
+
+        Returns:
+            True if there is an entry with this name in the the same section,
+                else False
+        """
+        return name in self.section.GetEntries()

tools/binman/etype/intel_descriptor.py

@@ -60,6 +60,10 @@ class Entry_intel_descriptor(Entry_blob):
         for i in range(MAX_REGIONS):
             self._regions.append(Region(self.data, frba, i))
 
-        # Set the offset for ME only, for now, since the others are not used
-        return {'intel-me': [self._regions[REGION_ME].base,
-                             self._regions[REGION_ME].size]}
+        # Set the offset for ME (Management Engine) only, for now, since the
+        # others are not used
+        info = {}
+        if self.HasSibling('intel-me'):
+            info['intel-me'] = [self._regions[REGION_ME].base,
+                                self._regions[REGION_ME].size]
+        return info

tools/binman/etype/intel_me.py

@@ -22,6 +22,8 @@ class Entry_intel_me(Entry_blob):
 
     A typical filename is 'me.bin'.
 
+    The position of this entry is generally set by the intel-descriptor entry.
+
     See README.x86 for information about x86 binary blobs.
     """
     def __init__(self, section, etype, node):