libcamera: v4l2_videodevice: Add a dequeue timer

Add a timer that gets reset on every buffer dequeue event. If the timeout
expires, optionally call a slot in the pipeline handler to handle this
condition. This may be useful in detecting and handling stalls in either the
hardware or device driver.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

include/libcamera/internal/v4l2_videodevice.h

@@ -20,7 +20,9 @@
 #include <libcamera/base/class.h>
 #include <libcamera/base/log.h>
 #include <libcamera/base/signal.h>
+#include <libcamera/base/timer.h>
 #include <libcamera/base/unique_fd.h>
+#include <libcamera/base/utils.h>
 
 #include <libcamera/color_space.h>
 #include <libcamera/framebuffer.h>
@@ -217,6 +219,9 @@ public:
 	int streamOn();
 	int streamOff();
 
+	void setDequeueTimeout(utils::Duration timeout);
+	Signal<> dequeueTimeout;
+
 	static std::unique_ptr<V4L2VideoDevice>
 	fromEntityName(const MediaDevice *media, const std::string &entity);
 
@@ -253,6 +258,8 @@ private:
 	void bufferAvailable();
 	FrameBuffer *dequeueBuffer();
 
+	void watchdogExpired();
+
 	V4L2Capability caps_;
 	V4L2DeviceFormat format_;
 	const PixelFormatInfo *formatInfo_;
@@ -266,6 +273,9 @@ private:
 	EventNotifier *fdBufferNotifier_;
 
 	State state_;
+
+	Timer watchdog_;
+	utils::Duration watchdogDuration_;
 };
 
 class V4L2M2MDevice

src/libcamera/v4l2_videodevice.cpp

@@ -539,6 +539,7 @@ V4L2VideoDevice::V4L2VideoDevice(const std::string &deviceNode)
 V4L2VideoDevice::V4L2VideoDevice(const MediaEntity *entity)
 	: V4L2VideoDevice(entity->deviceNode())
 {
+	watchdog_.timeout.connect(this, &V4L2VideoDevice::watchdogExpired);
 }
 
 V4L2VideoDevice::~V4L2VideoDevice()
@@ -1726,6 +1727,9 @@ FrameBuffer *V4L2VideoDevice::dequeueBuffer()
 		return nullptr;
 	}
 
+	if (watchdogDuration_.count())
+		watchdog_.start(std::chrono::duration_cast<std::chrono::milliseconds>(watchdogDuration_));
+
 	cache_->put(buf.index);
 
 	FrameBuffer *buffer = it->second;
@@ -1828,6 +1832,8 @@ int V4L2VideoDevice::streamOn()
 	}
 
 	state_ = State::Streaming;
+	if (watchdogDuration_.count())
+		watchdog_.start(std::chrono::duration_cast<std::chrono::milliseconds>(watchdogDuration_));
 
 	return 0;
 }
@@ -1852,6 +1858,9 @@ int V4L2VideoDevice::streamOff()
 	if (state_ != State::Streaming && queuedBuffers_.empty())
 		return 0;
 
+	if (watchdogDuration_.count())
+		watchdog_.stop();
+
 	ret = ioctl(VIDIOC_STREAMOFF, &bufferType_);
 	if (ret < 0) {
 		LOG(V4L2, Error)
@@ -1879,6 +1888,50 @@ int V4L2VideoDevice::streamOff()
 	return 0;
 }
 
+/**
+ * \brief Set the dequeue timeout value
+ * \param[in] timeout The timeout value to be used
+ *
+ * Sets a timeout value, given by \a timeout, that will be used by a watchdog
+ * timer to ensure buffer dequeue events are periodically occurring when the
+ * device is streaming. The watchdog timer is only active when the device is
+ * streaming, so it is not necessary to disable it when the device stops
+ * streaming. The timeout value can be safely updated at any time.
+ *
+ * If the timer expires, the \ref V4L2VideoDevice::dequeueTimeout signal is
+ * emitted. This can typically be used by pipeline handlers to be notified of
+ * stalled devices.
+ *
+ * Set \a timeout to 0 to disable the watchdog timer.
+ */
+void V4L2VideoDevice::setDequeueTimeout(utils::Duration timeout)
+{
+	watchdogDuration_ = timeout;
+
+	watchdog_.stop();
+	if (watchdogDuration_.count() && state_ == State::Streaming)
+		watchdog_.start(std::chrono::duration_cast<std::chrono::milliseconds>(timeout));
+}
+
+/**
+ * \var V4L2VideoDevice::dequeueTimeout
+ * \brief A Signal emitted when the dequeue watchdog timer expires
+ */
+
+/**
+ * \brief Slot to handle an expired dequeue timer
+ *
+ * When this slot is called, the time between successive dequeue events is over
+ * the required timeout. Emit the \ref V4L2VideoDevice::dequeueTimeout signal.
+ */
+void V4L2VideoDevice::watchdogExpired()
+{
+	LOG(V4L2, Warning)
+		<< "Dequeue timer of " << watchdogDuration_ << " has expired!";
+
+	dequeueTimeout.emit();
+}
+
 /**
  * \brief Create a new video device instance from \a entity in media device
  * \a media