[libcamera-devel] [PATCH v4 3/6] libcamera: device_enumerator: Emit a signal when a new devices are added

[Umang Jain]

Emit a signal whenever a new MediaDevices are added to the
DeviceEnumerator. This will allow CameraManager to be notified
about the new devices and it can re-emumerate all the devices
currently present on the system.

Device enumeration by the CameraManger is a expensive operation hence,
we want one signal emission per 'x' milliseconds to notify multiple
devices additions as a single batch, by the DeviceEnumerator.
Add a \todo to investigate the support for that.

Signed-off-by: Umang Jain <email at uajain.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 include/libcamera/internal/device_enumerator.h |  4 ++++
 src/libcamera/camera_manager.cpp               |  4 ++--
 src/libcamera/device_enumerator.cpp            | 13 +++++++++++++
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/include/libcamera/internal/device_enumerator.h b/include/libcamera/internal/device_enumerator.h
index 25a3630..a985040 100644
--- a/include/libcamera/internal/device_enumerator.h
+++ b/include/libcamera/internal/device_enumerator.h
@@ -13,6 +13,8 @@
 
 #include <linux/media.h>
 
+#include <libcamera/signal.h>
+
 namespace libcamera {
 
 class MediaDevice;
@@ -43,6 +45,8 @@ public:
 
 	std::shared_ptr<MediaDevice> search(const DeviceMatch &dm);
 
+	Signal<> devicesAdded;
+
 protected:
 	std::unique_ptr<MediaDevice> createDevice(const std::string &deviceNode);
 	void addDevice(std::unique_ptr<MediaDevice> &&media);
diff --git a/src/libcamera/camera_manager.cpp b/src/libcamera/camera_manager.cpp
index aba5a0c..17a4afb 100644
--- a/src/libcamera/camera_manager.cpp
+++ b/src/libcamera/camera_manager.cpp
@@ -155,12 +155,12 @@ void CameraManager::Private::createPipelineHandlers()
 		}
 	}
 
-	/* \todo Register hot-plug callback here */
+	enumerator_->devicesAdded.connect(this, &Private::createPipelineHandlers);
 }
 
 void CameraManager::Private::cleanup()
 {
-	/* \todo Unregister hot-plug callback here */
+	enumerator_->devicesAdded.disconnect(this, &Private::createPipelineHandlers);
 
 	/*
 	 * Release all references to cameras and pipeline handlers to ensure
diff --git a/src/libcamera/device_enumerator.cpp b/src/libcamera/device_enumerator.cpp
index e21a2a7..e3264a5 100644
--- a/src/libcamera/device_enumerator.cpp
+++ b/src/libcamera/device_enumerator.cpp
@@ -227,6 +227,16 @@ std::unique_ptr<MediaDevice> DeviceEnumerator::createDevice(const std::string &d
 	return media;
 }
 
+/**
+* \var DeviceEnumerator::devicesAdded
+* \brief Notify of new media devices being found
+*
+* This signal is emitted when the device enumerator finds new media devices in
+* the system. It may be emitted for every newly detected device, or once for
+* multiple of devices, at the discretion of the device enumerator. Not all
+* device enumerator types may support dynamic detection of new devices.
+*/
+
 /**
  * \brief Add a media device to the enumerator
  * \param[in] media media device instance to add
@@ -242,6 +252,9 @@ void DeviceEnumerator::addDevice(std::unique_ptr<MediaDevice> &&media)
 		<< "Added device " << media->deviceNode() << ": " << media->driver();
 
 	devices_.push_back(std::move(media));
+
+	/* \todo To batch multiple additions, emit with a small delay here. */
+	devicesAdded.emit();
 }
 
 /**
-- 
2.26.2