libcamera: v4l2_videodevice: Add support for frame start events

Extend the V4L2VideoDevice to support notifying of frame start events.
The events are received from the device through the V4L2 event API, and
passed to users of the class through a signal.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

2 files changed, 82 insertions, 1 deletions

diff --git a/src/libcamera/include/v4l2_videodevice.h b/src/libcamera/include/v4l2_videodevice.h
index ee63d28d..a0409e59 100644
--- a/src/libcamera/include/v4l2_videodevice.h
+++ b/src/libcamera/include/v4l2_videodevice.h
@@ -224,6 +224,9 @@ public:
 	int queueBuffer(FrameBuffer *buffer);
 	Signal<FrameBuffer *> bufferReady;
 
+	int setFrameStartEnabled(bool enable);
+	Signal<uint32_t> frameStart;
+
 	int streamOn();
 	int streamOff();
 
@@ -262,6 +265,8 @@ private:
 	void bufferAvailable(EventNotifier *notifier);
 	FrameBuffer *dequeueBuffer();
 
+	void eventAvailable(EventNotifier *notifier);
+
 	V4L2Capability caps_;
 
 	enum v4l2_buf_type bufferType_;
@@ -271,6 +276,9 @@ private:
 	std::map<unsigned int, FrameBuffer *> queuedBuffers_;
 
 	EventNotifier *fdBufferNotifier_;
+	EventNotifier *fdEventNotifier_;
+
+	bool frameStartEnabled_;
 };
 
 class V4L2M2MDevice
diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index fae4f078..8d642be0 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -544,7 +544,8 @@ const std::string V4L2DeviceFormat::toString() const
  * \param[in] deviceNode The file-system path to the video device node
  */
 V4L2VideoDevice::V4L2VideoDevice(const std::string &deviceNode)
-	: V4L2Device(deviceNode), cache_(nullptr), fdBufferNotifier_(nullptr)
+	: V4L2Device(deviceNode), cache_(nullptr), fdBufferNotifier_(nullptr),
+	  fdEventNotifier_(nullptr), frameStartEnabled_(false)
 {
 	/*
 	 * We default to an MMAP based CAPTURE video device, however this will
@@ -637,6 +638,10 @@ int V4L2VideoDevice::open()
 	fdBufferNotifier_->activated.connect(this, &V4L2VideoDevice::bufferAvailable);
 	fdBufferNotifier_->setEnabled(false);
 
+	fdEventNotifier_ = new EventNotifier(fd(), EventNotifier::Exception);
+	fdEventNotifier_->activated.connect(this, &V4L2VideoDevice::eventAvailable);
+	fdEventNotifier_->setEnabled(false);
+
 	LOG(V4L2, Debug)
 		<< "Opened device " << caps_.bus_info() << ": "
 		<< caps_.driver() << ": " << caps_.card();
@@ -726,6 +731,10 @@ int V4L2VideoDevice::open(int handle, enum v4l2_buf_type type)
 	fdBufferNotifier_->activated.connect(this, &V4L2VideoDevice::bufferAvailable);
 	fdBufferNotifier_->setEnabled(false);
 
+	fdEventNotifier_ = new EventNotifier(fd(), EventNotifier::Exception);
+	fdEventNotifier_->activated.connect(this, &V4L2VideoDevice::eventAvailable);
+	fdEventNotifier_->setEnabled(false);
+
 	LOG(V4L2, Debug)
 		<< "Opened device " << caps_.bus_info() << ": "
 		<< caps_.driver() << ": " << caps_.card();
@@ -743,6 +752,7 @@ void V4L2VideoDevice::close()
 
 	releaseBuffers();
 	delete fdBufferNotifier_;
+	delete fdEventNotifier_;
 
 	V4L2Device::close();
 }
@@ -1571,11 +1581,74 @@ FrameBuffer *V4L2VideoDevice::dequeueBuffer()
 }
 
 /**
+ * \brief Slot to handle V4L2 events from the V4L2 video device
+ * \param[in] notifier The event notifier
+ *
+ * When this slot is called, a V4L2 event is available to be dequeued from the
+ * device.
+ */
+void V4L2VideoDevice::eventAvailable(EventNotifier *notifier)
+{
+	struct v4l2_event event{};
+	int ret = ioctl(VIDIOC_DQEVENT, &event);
+	if (ret < 0) {
+		LOG(V4L2, Error)
+			<< "Failed to dequeue event, disabling event notifier";
+		fdEventNotifier_->setEnabled(false);
+		return;
+	}
+
+	if (event.type != V4L2_EVENT_FRAME_SYNC) {
+		LOG(V4L2, Error)
+			<< "Spurious event (" << event.type
+			<< "), disabling event notifier";
+		fdEventNotifier_->setEnabled(false);
+		return;
+	}
+
+	frameStart.emit(event.u.frame_sync.frame_sequence);
+}
+
+/**
  * \var V4L2VideoDevice::bufferReady
  * \brief A Signal emitted when a framebuffer completes
  */
 
 /**
+ * \brief Enable or disable frame start event notification
+ * \param[in] enable True to enable frame start events, false to disable them
+ *
+ * This function enables or disables generation of frame start events. Once
+ * enabled, the events are signalled through the frameStart signal.
+ *
+ * \return 0 on success, a negative error code otherwise
+ */
+int V4L2VideoDevice::setFrameStartEnabled(bool enable)
+{
+	if (frameStartEnabled_ == enable)
+		return 0;
+
+	struct v4l2_event_subscription event{};
+	event.type = V4L2_EVENT_FRAME_SYNC;
+
+	unsigned long request = enable ? VIDIOC_SUBSCRIBE_EVENT
+			      : VIDIOC_UNSUBSCRIBE_EVENT;
+	int ret = ioctl(request, &event);
+	if (enable && ret)
+		return ret;
+
+	fdEventNotifier_->setEnabled(enable);
+	frameStartEnabled_ = enable;
+
+	return ret;
+}
+
+/**
+ * \var V4L2VideoDevice::frameStart
+ * \brief A Signal emitted when capture of a frame has started
+ */
+
+/**
  * \brief Start the video stream
  * \return 0 on success or a negative error code otherwise
  */