device: simplify structure of handles array

Force the inclusion of a `DEVICE_HANDLE_SEP` at the end of the
devicetree dependency section of the array. This lets us simplify the
implementation of `device_required_handles_get`, as there is only one
symbol the section ends with.

This does not use any extra ROM as the array is padded out to the
original size with `DEVICE_HANDLE_ENDS` anyway.

Also adds a description of the array format where the array is
instantiated.

Signed-off-by: Jordan Yates <[email protected]>

Author: Jordan Yates

include/device.h

@@ -478,8 +478,7 @@ device_required_handles_get(const struct device *dev,
 	if (rv != NULL) {
 		size_t i = 0;
 
-		while ((rv[i] != DEVICE_HANDLE_ENDS)
-		       && (rv[i] != DEVICE_HANDLE_SEP)) {
+		while (rv[i] != DEVICE_HANDLE_SEP) {
 			++i;
 		}
 		*count = i;
@@ -674,6 +673,22 @@ static inline bool device_is_ready(const struct device *dev)
  * in a distinct pass1 section (which will be replaced by
  * postprocessing).
  *
+ * Before processing in gen_handles.py, the array format is:
+ * {
+ *     DEVICE_ORDINAL (or DEVICE_HANDLE_NULL if not a devicetree node),
+ *     List of devicetree dependency ordinals (if any),
+ *     DEVICE_HANDLE_SEP,
+ *     List of injected dependency ordinals (if any),
+ * }
+ *
+ * After processing in gen_handles.py, the format is updated to:
+ * {
+ *     List of existing devicetree dependency handles (if any),
+ *     DEVICE_HANDLE_SEP,
+ *     List of injected dependency ordinals (if any),
+ *     DEVICE_HANDLE_NULL padding to original length (at least one)
+ * }
+ *
  * It is also (experimentally) necessary to provide explicit alignment
  * on each object. Otherwise x86-64 builds will introduce padding
  * between objects in the same input section in individual object

scripts/gen_handles.py

@@ -294,10 +294,11 @@ def main():
                         dep_paths.append(dn.path)
                     else:
                         dep_paths.append('(%s)' % dn.path)
+            # Force separator to signal start of injected dependencies
+            hdls.append(DEVICE_HANDLE_SEP)
             if len(hs.ext_deps) > 0:
                 # TODO: map these to something smaller?
                 ext_paths.extend(map(str, hs.ext_deps))
-                hdls.append(DEVICE_HANDLE_SEP)
                 hdls.extend(hs.ext_deps)
 
             # When CONFIG_USERSPACE is enabled the pre-built elf is