[libcamera-devel] [PATCH v5 3/6] libcamera: device_enumerator: Emit a signal when new devices are added

[Umang Jain]

Emit a signal whenever 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 an 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>
Reviewed-by: Kieran Bingham <kieran.bingham 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 de6d5d8..3082797 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 to ensure they all get destroyed
diff --git a/src/libcamera/device_enumerator.cpp b/src/libcamera/device_enumerator.cpp
index e21a2a7..647974b 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 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