[libcamera-devel] [PATCH v2 1/2] libcamera: v4l2_videodevice: Add a dequeue timer

[Naushir Patuck]

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 at raspberrypi.com>
---
 include/libcamera/internal/v4l2_videodevice.h | 10 ++++
 src/libcamera/v4l2_videodevice.cpp            | 49 +++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/include/libcamera/internal/v4l2_videodevice.h b/include/libcamera/internal/v4l2_videodevice.h
index 2d2ccc477c91..c34cc6585612 100644
--- a/include/libcamera/internal/v4l2_videodevice.h
+++ b/include/libcamera/internal/v4l2_videodevice.h
@@ -9,6 +9,7 @@
 
 #include <array>
 #include <atomic>
+#include <chrono>
 #include <memory>
 #include <optional>
 #include <stdint.h>
@@ -20,6 +21,7 @@
 #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/color_space.h>
@@ -216,6 +218,9 @@ public:
 	int streamOn();
 	int streamOff();
 
+	void setDequeueTimeout(std::chrono::milliseconds msec);
+	Signal<> dequeueTimeout;
+
 	static std::unique_ptr<V4L2VideoDevice>
 	fromEntityName(const MediaDevice *media, const std::string &entity);
 
@@ -246,6 +251,8 @@ private:
 	void bufferAvailable();
 	FrameBuffer *dequeueBuffer();
 
+	void watchdogExpired();
+
 	V4L2Capability caps_;
 	V4L2DeviceFormat format_;
 	const PixelFormatInfo *formatInfo_;
@@ -259,6 +266,9 @@ private:
 	EventNotifier *fdBufferNotifier_;
 
 	bool streaming_;
+
+	Timer watchdog_;
+	std::chrono::milliseconds watchdogDuration_;
 };
 
 class V4L2M2MDevice
diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index 5f36ee20710d..29225f3058b0 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -526,6 +526,7 @@ V4L2VideoDevice::V4L2VideoDevice(const std::string &deviceNode)
 V4L2VideoDevice::V4L2VideoDevice(const MediaEntity *entity)
 	: V4L2VideoDevice(entity->deviceNode())
 {
+	watchdog_.timeout.connect(this, &V4L2VideoDevice::watchdogExpired);
 }
 
 V4L2VideoDevice::~V4L2VideoDevice()
@@ -1695,6 +1696,9 @@ FrameBuffer *V4L2VideoDevice::dequeueBuffer()
 		return nullptr;
 	}
 
+	if (watchdogDuration_.count())
+		watchdog_.start(watchdogDuration_);
+
 	cache_->put(buf.index);
 
 	FrameBuffer *buffer = it->second;
@@ -1797,6 +1801,8 @@ int V4L2VideoDevice::streamOn()
 	}
 
 	streaming_ = true;
+	if (watchdogDuration_.count())
+		watchdog_.start(watchdogDuration_);
 
 	return 0;
 }
@@ -1821,6 +1827,9 @@ int V4L2VideoDevice::streamOff()
 	if (!streaming_ && queuedBuffers_.empty())
 		return 0;
 
+	if (watchdogDuration_.count())
+		watchdog_.stop();
+
 	ret = ioctl(VIDIOC_STREAMOFF, &bufferType_);
 	if (ret < 0) {
 		LOG(V4L2, Error)
@@ -1843,6 +1852,46 @@ int V4L2VideoDevice::streamOff()
 	return 0;
 }
 
+/**
+ * \brief Set the dequeue timeout value
+ * \param[in] msec The timeout value to be used
+ *
+ * Sets a timeout value, given by \a msec, 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 msec to 0 to disable the watchdog timer.
+ */
+void V4L2VideoDevice::setDequeueTimeout(std::chrono::milliseconds msec)
+{
+	watchdogDuration_ = msec;
+
+	watchdog_.stop();
+	if (watchdogDuration_.count() && streaming_)
+		watchdog_.start(msec);
+}
+
+/**
+ * \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_.count()
+		<< " ms has expired!";
+
+	dequeueTimeout.emit();
+}
+
 /**
  * \brief Create a new video device instance from \a entity in media device
  * \a media
-- 
2.25.1