libcamera: Add 'required' property to controls

Add to the ControlId class a 'required' boolean flag that determine
if the control (or property) is mandatory to be supported by a Camera
in order to comply with the libcamera API specification.

Add support for a 'required' field to the controls and properties yaml
file definition and control generation scripts.

Also plumb support for the flag in the control serializer component
to allow pass the information across IPC borders.

Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

8 files changed, 48 insertions, 18 deletions

diff --git a/Documentation/guides/pipeline-handler.rst b/Documentation/guides/pipeline-handler.rst
index 26dc9358..ad2a5beb 100644
--- a/Documentation/guides/pipeline-handler.rst
+++ b/Documentation/guides/pipeline-handler.rst
@@ -610,10 +610,15 @@ information can be found in the `ControlInfoMap`_ class documentation.
 .. _ControlInfoMap: https://libcamera.org/api-html/classlibcamera_1_1ControlInfoMap.html
 
 Pipeline handlers register controls to expose the tunable device and IPA
-parameters to applications. Our example pipeline handler only exposes trivial
-controls of the video device, by registering a ``ControlId`` instance with
-associated values for each supported V4L2 control but demonstrates the mapping
-of V4L2 Controls to libcamera ControlIDs.
+parameters to applications and register properties to expose the Camera
+immutable characteristics. Controls and properties which have the ``required``
+field specified in the YAML definition are mandatory to be supported by a Camera
+in order for it to comply with the libcamera API specification.
+
+Our example pipeline handler only exposes trivial controls of the video device,
+by registering a ``ControlId`` instance with associated values for each
+supported V4L2 control but demonstrates the mapping of V4L2 Controls to
+libcamera ControlIDs.
 
 Complete the initialization of the ``VividCameraData`` class by adding the
 following code to the ``VividCameraData::init()`` function to initialise the
diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
index cf942055..01821191 100644
--- a/include/libcamera/controls.h
+++ b/include/libcamera/controls.h
@@ -213,14 +213,15 @@ private:
 class ControlId
 {
 public:
-	ControlId(unsigned int id, const std::string &name, ControlType type)
-		: id_(id), name_(name), type_(type)
+	ControlId(unsigned int id, const std::string &name, ControlType type, bool required)
+		: id_(id), name_(name), type_(type), required_(required)
 	{
 	}
 
 	unsigned int id() const { return id_; }
 	const std::string &name() const { return name_; }
 	ControlType type() const { return type_; }
+	bool required() const { return required_; }
 
 private:
 	LIBCAMERA_DISABLE_COPY_AND_MOVE(ControlId)
@@ -228,6 +229,7 @@ private:
 	unsigned int id_;
 	std::string name_;
 	ControlType type_;
+	bool required_;
 };
 
 static inline bool operator==(unsigned int lhs, const ControlId &rhs)
@@ -256,8 +258,8 @@ class Control : public ControlId
 public:
 	using type = T;
 
-	Control(unsigned int id, const char *name)
-		: ControlId(id, name, details::control_type<std::remove_cv_t<T>>::value)
+	Control(unsigned int id, const char *name, bool required)
+		: ControlId(id, name, details::control_type<std::remove_cv_t<T>>::value, required)
 	{
 	}
 
diff --git a/include/libcamera/ipa/ipa_controls.h b/include/libcamera/ipa/ipa_controls.h
index e5da1946..5268b0a8 100644
--- a/include/libcamera/ipa/ipa_controls.h
+++ b/include/libcamera/ipa/ipa_controls.h
@@ -46,7 +46,8 @@ struct ipa_control_info_entry {
 	uint32_t id;
 	uint32_t type;
 	uint32_t offset;
-	uint32_t padding[1];
+	uint8_t required;
+	uint8_t padding[3];
 };
 
 #ifdef __cplusplus
diff --git a/src/libcamera/control_serializer.cpp b/src/libcamera/control_serializer.cpp
index 0cf719bd..b9ed1eea 100644
--- a/src/libcamera/control_serializer.cpp
+++ b/src/libcamera/control_serializer.cpp
@@ -281,6 +281,7 @@ int ControlSerializer::serialize(const ControlInfoMap &infoMap,
 		entry.id = id->id();
 		entry.type = id->type();
 		entry.offset = values.offset();
+		entry.required = id->required();
 		entries.write(&entry);
 
 		store(info, values);
@@ -498,7 +499,8 @@ ControlInfoMap ControlSerializer::deserialize<ControlInfoMap>(ByteStreamBuffer &
 			 * debugging purpose.
 			 */
 			controlIds_.emplace_back(std::make_unique<ControlId>(entry->id,
-									     "", type));
+									     "", type,
+									     entry->required));
 			(*localIdMap)[entry->id] = controlIds_.back().get();
 		}
 
diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp
index b808116c..25f30953 100644
--- a/src/libcamera/controls.cpp
+++ b/src/libcamera/controls.cpp
@@ -378,18 +378,19 @@ void ControlValue::reserve(ControlType type, bool isArray, std::size_t numElemen
  * \class ControlId
  * \brief Control static metadata
  *
- * The ControlId class stores a control ID, name and data type. It provides
- * unique identification of a control, but without support for compile-time
- * type deduction that the derived template Control class supports. See the
- * Control class for more information.
+ * The ControlId class stores a control ID, name, data type and a boolean
+ * 'required' flag. It provides unique identification of a control, but without
+ * support for compile-time type deduction that the derived template Control
+ * class supports. See the Control class for more information.
  */
 
 /**
- * \fn ControlId::ControlId(unsigned int id, const std::string &name, ControlType type)
+ * \fn ControlId::ControlId(unsigned int id, const std::string &name, ControlType type, bool required)
  * \brief Construct a ControlId instance
  * \param[in] id The control numerical ID
  * \param[in] name The control name
  * \param[in] type The control data type
+ * \param[in] required Boolean flag that determine if the control is required
  */
 
 /**
@@ -411,6 +412,16 @@ void ControlValue::reserve(ControlType type, bool isArray, std::size_t numElemen
  */
 
 /**
+ * \fn bool ControlId::required() const
+ * \brief Determine if the control is required or not
+ *
+ * A control is 'required' if it is mandatory for a Camera to support it to
+ * comply with the libcamera API specification.
+ *
+ * \return True if the control is required, false otherwise
+ */
+
+/**
  * \fn bool operator==(unsigned int lhs, const ControlId &rhs)
  * \brief Compare a ControlId with a control numerical ID
  * \param[in] lhs Left-hand side numerical ID
@@ -456,10 +467,11 @@ void ControlValue::reserve(ControlType type, bool isArray, std::size_t numElemen
  */
 
 /**
- * \fn Control::Control(unsigned int id, const char *name)
+ * \fn Control::Control(unsigned int id, const char *name, bool required)
  * \brief Construct a Control instance
  * \param[in] id The control numerical ID
  * \param[in] name The control name
+ * \param[in] required Boolean flag that determine if a control is required
  *
  * The control data type is automatically deduced from the template type T.
  */
diff --git a/src/libcamera/ipa_controls.cpp b/src/libcamera/ipa_controls.cpp
index 870a443b..2376cbd9 100644
--- a/src/libcamera/ipa_controls.cpp
+++ b/src/libcamera/ipa_controls.cpp
@@ -220,6 +220,8 @@ static_assert(sizeof(ipa_control_value_entry) == 16,
  * \var ipa_control_info_entry::offset
  * The offset in bytes from the beginning of the data section to the control
  * info data (shall be a multiple of 8 bytes)
+ * \var ipa_control_info_entry::required
+ * Boolean flag that determines if the controls is required or not
  * \var ipa_control_info_entry::padding
  * Padding bytes (shall be set to 0)
  */
diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
index 24d208ef..b055d14c 100644
--- a/src/libcamera/v4l2_device.cpp
+++ b/src/libcamera/v4l2_device.cpp
@@ -522,7 +522,7 @@ std::unique_ptr<ControlId> V4L2Device::v4l2ControlId(const v4l2_query_ext_ctrl &
 	const std::string name(static_cast<const char *>(ctrl.name), len);
 	const ControlType type = v4l2CtrlType(ctrl.type);
 
-	return std::make_unique<ControlId>(ctrl.id, name, type);
+	return std::make_unique<ControlId>(ctrl.id, name, type, false);
 }
 
 /**
diff --git a/utils/gen-controls.py b/utils/gen-controls.py
index 6cd5e362..1e997708 100755
--- a/utils/gen-controls.py
+++ b/utils/gen-controls.py
@@ -112,6 +112,11 @@ class Control(object):
         else:
             return f"Span<const {typ}>"
 
+    @property
+    def required(self):
+        """Is the control required"""
+        return self.__data.get('required')
+
 
 def snake_case(s):
     return ''.join([c.isupper() and ('_' + c) or c for c in s]).strip('_')
@@ -133,7 +138,7 @@ ${description}''')
  * \\var ${name}
 ${description}
  */''')
-    def_template = string.Template('extern const Control<${type}> ${name}(${id_name}, "${name}");')
+    def_template = string.Template('extern const Control<${type}> ${name}(${id_name}, "${name}", ${required});')
     enum_values_doc = string.Template('''/**
  * \\var ${name}Values
  * \\brief List of all $name supported values
@@ -158,6 +163,7 @@ ${description}
             'type': ctrl.type,
             'description': format_description(ctrl.description),
             'id_name': id_name,
+            'required': "true" if ctrl.required else "false"
         }
 
         target_doc = ctrls_doc[vendor]