libcamera: controls: Handle enum values without a cast

When constructing a ControlValue from an enum value, an explicit cast to
int32_t is needed as we use int32_t as the underlying type for all
enumerated controls. This makes users of ControlValue more complex. To
simplify them, specialize the control_type template for enum types, to
support construction of ControlValue directly without a cast.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/controls.h

@@ -39,7 +39,7 @@ enum ControlType {
 
 namespace details {
 
-template<typename T>
+template<typename T, typename = std::void_t<>>
 struct control_type {
 };
 
@@ -102,6 +102,10 @@ struct control_type<Span<T, N>> : public control_type<std::remove_cv_t<T>> {
 	static constexpr std::size_t size = N;
 };
 
+template<typename T>
+struct control_type<T, std::enable_if_t<std::is_enum_v<T>>> : public control_type<int32_t> {
+};
+
 } /* namespace details */
 
 class ControlValue

src/libcamera/pipeline/ipu3/ipu3.cpp

@@ -958,7 +958,7 @@ int PipelineHandlerIPU3::updateControls(IPU3CameraData *data)
 		values.reserve(testPatternModes.size());
 
 		for (auto pattern : testPatternModes)
-			values.emplace_back(static_cast<int32_t>(pattern));
+			values.emplace_back(pattern);
 
 		controls[&controls::draft::TestPatternMode] = ControlInfo(values);
 	}