utils: ipc: Allow the skipHeader attribute on enums

Currently, enums that are passed between pipeline handlers and their IPA
must be defined in a mojom file. However, there is a use case for
enum/flags to be defined in a C++ header, such that the enum can be used
in a component other than the pipeline handler and its IPA.

To support this, add support for the skipHeader attribute for enums.
Like structs, it is only allowed in core.mojom.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

include/libcamera/ipa/core.mojom

@@ -14,8 +14,8 @@ module libcamera;
  * - structs
  *
  * Attributes:
- * - skipHeader - structs only, and only in core.mojom
- *   - Do not generate a C++ definition for the structure
+ * - skipHeader - allowed only for structs and enums in core.mojom
+ *   - Do not generate a C++ definition for the structure or enum
  *   - Any type used in a mojom interface definition must have a corresponding
  *     definition in a mojom file for the code generator to accept it, except
  *     for types solely used as map/array members for which a definition is not
@@ -52,6 +52,8 @@ module libcamera;
  *   then the type definition in the core.mojom file should have the
  *   [skipHeader] attribute only
  *   - A (de)serializer will be generated for the type
+ *   - enums that are defined in a libcamera C++ header also fall in this
+ *     category
  * - If a type definition has [skipHeader], then the header where the type is
  *   defined must be included in ipa_interface.h
  * - Types that are solely used as array/map members do not require a mojom

include/libcamera/ipa/ipa_interface.h

@@ -23,8 +23,8 @@
 namespace libcamera {
 
 /*
- * Structs that are defined in core.mojom and have the skipHeader tag must be
- * #included here.
+ * Structs and enums that are defined in core.mojom that have the skipHeader
+ * tag must be #included here.
  */
 
 class IPAInterface

utils/ipc/generators/libcamera_templates/core_ipa_interface.h.tmpl

@@ -26,7 +26,7 @@ namespace libcamera {
 static const {{const.kind|name}} {{const.mojom_name}} = {{const.value}};
 {% endfor %}
 
-{% for enum in enums %}
+{% for enum in enums_gen_header %}
 {{funcs.define_enum(enum)}}
 {% endfor %}
 

utils/ipc/generators/mojom_libcamera_generator.py

@@ -483,7 +483,7 @@ def _GetJinjaExports(self):
     def _GetJinjaExportsForCore(self):
         return {
             'consts': self.module.constants,
-            'enums': self.module.enums,
+            'enums_gen_header': [x for x in self.module.enums if x.attributes is None or 'skipHeader' not in x.attributes],
             'has_array': len([x for x in self.module.kinds.keys() if x[0] == 'a']) > 0,
             'has_map': len([x for x in self.module.kinds.keys() if x[0] == 'm']) > 0,
             'structs_gen_header': [x for x in self.module.structs if x.attributes is None or 'skipHeader' not in x.attributes],