[PATCH v2 2/2] libcamera: camera_manager: Add environment variable to order pipelines match

[Julien Vuillaumier]

To match the enumerated media devices, each pipeline handler registered
is used in no specific order. It is a limitation when several pipelines
can match the devices, and user has to select a specific pipeline.

For this purpose, environment variable LIBCAMERA_PIPELINES_MATCH_LIST is
created that gives the option to define an ordered list of pipelines
to invoke during the match process.

LIBCAMERA_PIPELINES_MATCH_LIST="<name1>[,<name2>[,<name3>...]]]"

Example:
LIBCAMERA_PIPELINES_MATCH_LIST="PipelineHandlerRkISP1,SimplePipelineHandler"

Signed-off-by: Julien Vuillaumier <julien.vuillaumier at nxp.com>
---
 Documentation/environment_variables.rst     |  5 ++
 include/libcamera/internal/camera_manager.h |  1 +
 src/libcamera/camera_manager.cpp            | 57 ++++++++++++++++-----
 3 files changed, 51 insertions(+), 12 deletions(-)

diff --git a/Documentation/environment_variables.rst b/Documentation/environment_variables.rst
index a9b230bc..ea4da3c9 100644
--- a/Documentation/environment_variables.rst
+++ b/Documentation/environment_variables.rst
@@ -37,6 +37,11 @@ LIBCAMERA_IPA_MODULE_PATH
 
    Example value: ``${HOME}/.libcamera/lib:/opt/libcamera/vendor/lib``
 
+LIBCAMERA_PIPELINES_MATCH_LIST
+   Define an ordered list of pipeline names to be used to match the media devices in the system.
+
+   Example value: ``PipelineHandlerRkISP1,SimplePipelineHandler``
+
 LIBCAMERA_RPI_CONFIG_FILE
    Define a custom configuration file to use in the Raspberry Pi pipeline handler.
 
diff --git a/include/libcamera/internal/camera_manager.h b/include/libcamera/internal/camera_manager.h
index 33ebe069..c57e509a 100644
--- a/include/libcamera/internal/camera_manager.h
+++ b/include/libcamera/internal/camera_manager.h
@@ -45,6 +45,7 @@ private:
 	int init();
 	void createPipelineHandlers();
 	void cleanup() LIBCAMERA_TSA_EXCLUDES(mutex_);
+	void pipelineFactoryMatch(const PipelineHandlerFactoryBase *factory);
 
 	/*
 	 * This mutex protects
diff --git a/src/libcamera/camera_manager.cpp b/src/libcamera/camera_manager.cpp
index 355f3ada..620be1c8 100644
--- a/src/libcamera/camera_manager.cpp
+++ b/src/libcamera/camera_manager.cpp
@@ -99,13 +99,36 @@ int CameraManager::Private::init()
 
 void CameraManager::Private::createPipelineHandlers()
 {
-	CameraManager *const o = LIBCAMERA_O_PTR();
-
 	/*
 	 * \todo Try to read handlers and order from configuration
-	 * file and only fallback on all handlers if there is no
-	 * configuration file.
+	 * file and only fallback on environment variable or all handlers, if
+	 * there is no configuration file.
+	 */
+
+	/*
+	 * When a list of preferred pipelines is defined, iterate through the
+	 * ordered list to match the devices enumerated.
+	 * Otherwise, device matching is done in no specific order with each
+	 * registered pipeline handler.
 	 */
+	const char *pipesList =
+		utils::secure_getenv("LIBCAMERA_PIPELINES_MATCH_LIST");
+	if (pipesList) {
+		for (const auto &pipeName : utils::split(pipesList, ",")) {
+			const PipelineHandlerFactoryBase *factory;
+			factory = PipelineHandlerFactoryBase::getFactoryByName(pipeName);
+			if (!factory)
+				continue;
+
+			LOG(Camera, Debug)
+				<< "Found listed pipeline handler '"
+				<< pipeName << "'";
+			pipelineFactoryMatch(factory);
+		}
+
+		return;
+	}
+
 	const std::vector<PipelineHandlerFactoryBase *> &factories =
 		PipelineHandlerFactoryBase::factories();
 
@@ -117,15 +140,25 @@ void CameraManager::Private::createPipelineHandlers()
 		 * Try each pipeline handler until it exhaust
 		 * all pipelines it can provide.
 		 */
-		while (1) {
-			std::shared_ptr<PipelineHandler> pipe = factory->create(o);
-			if (!pipe->match(enumerator_.get()))
-				break;
+		pipelineFactoryMatch(factory);
+	}
+}
 
-			LOG(Camera, Debug)
-				<< "Pipeline handler \"" << factory->name()
-				<< "\" matched";
-		}
+void CameraManager::Private::pipelineFactoryMatch(const PipelineHandlerFactoryBase *factory)
+{
+	CameraManager *const o = LIBCAMERA_O_PTR();
+
+	/*
+	 * Provide as many matching pipelines as possible
+	 */
+	while (1) {
+		std::shared_ptr<PipelineHandler> pipe = factory->create(o);
+		if (!pipe->match(enumerator_.get()))
+			break;
+
+		LOG(Camera, Debug)
+			<< "Pipeline handler \"" << factory->name()
+			<< "\" matched";
 	}
 }
 
-- 
2.34.1