[libcamera-devel] [PATCH v4 4/4] ipa: raspberrypi: Rate-limit the controller algorithms

[Naushir Patuck]

The controller algorithms currently run on every frame provided to the
IPA by the pipeline handler. This may be undesirable for very fast fps
operating modes where it could significantly increase the computation
cycles (per unit time) without providing any significant changes to the
IQ parameters. The added latencies could also cause dropped frames.

Pass the FrameBuffer timestamp to the IPA through the controls. This
timestamp will be used to rate-limit the controller algorithms to run
with a minimum inter-frame time given by a compile time constant,
currently set to 16.66ms. On startup, we don't rate-limit the algorithms
until after the number of frames required for convergence.

Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
---
 src/ipa/raspberrypi/raspberrypi.cpp           | 50 +++++++++++++++++--
 .../pipeline/raspberrypi/raspberrypi.cpp      |  5 ++
 2 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/src/ipa/raspberrypi/raspberrypi.cpp b/src/ipa/raspberrypi/raspberrypi.cpp
index f6d1ab16a290..eac1cf8cfe44 100644
--- a/src/ipa/raspberrypi/raspberrypi.cpp
+++ b/src/ipa/raspberrypi/raspberrypi.cpp
@@ -61,6 +61,14 @@ constexpr unsigned int DefaultExposureTime = 20000;
 constexpr double defaultMinFrameDuration = 1e6 / 30.0;
 constexpr double defaultMaxFrameDuration = 1e6 / 0.01;
 
+/*
+ * Determine the minimum allowable inter-frame duration (in us) to run the
+ * controller algorithms. If the pipeline handler provider frames at a rate
+ * higher than this, we rate-limit the controller Prepare() and Process() calls
+ * to lower than or equal to this rate.
+ */
+constexpr double controllerMinFrameDuration = 1e6 / 60.0;
+
 LOG_DEFINE_CATEGORY(IPARPI)
 
 class IPARPi : public ipa::RPi::IPARPiInterface
@@ -68,7 +76,7 @@ class IPARPi : public ipa::RPi::IPARPiInterface
 public:
 	IPARPi()
 		: controller_(), frameCount_(0), checkCount_(0), mistrustCount_(0),
-		  lsTable_(nullptr), firstStart_(true)
+		  lastRunTimestamp_(0), lsTable_(nullptr), firstStart_(true)
 	{
 	}
 
@@ -146,6 +154,12 @@ private:
 	/* Number of frames that need to be dropped on startup. */
 	unsigned int dropFrameCount_;
 
+	/* Frame timestamp for the last run of the controller. */
+	uint64_t lastRunTimestamp_;
+
+	/* Do we run a Controller::process() for this frame? */
+	bool processPending_;
+
 	/* LS table allocation passed in from the pipeline handler. */
 	FileDescriptor lsTableHandle_;
 	void *lsTable_;
@@ -262,6 +276,7 @@ void IPARPi::start(const ControlList &controls, ipa::RPi::StartConfig *startConf
 	startConfig->dropFrameCount = dropFrameCount_;
 
 	firstStart_ = false;
+	lastRunTimestamp_ = 0;
 }
 
 void IPARPi::setMode(const CameraSensorInfo &sensorInfo)
@@ -406,7 +421,7 @@ void IPARPi::signalStatReady(uint32_t bufferId)
 {
 	if (++checkCount_ != frameCount_) /* assert here? */
 		LOG(IPARPI, Error) << "WARNING: Prepare/Process mismatch!!!";
-	if (frameCount_ > mistrustCount_)
+	if (processPending_ && frameCount_ > mistrustCount_)
 		processStats(bufferId);
 
 	reportMetadata();
@@ -894,10 +909,11 @@ void IPARPi::returnEmbeddedBuffer(unsigned int bufferId)
 
 void IPARPi::prepareISP(const ipa::RPi::ISPConfig &data)
 {
+	int64_t frameTimestamp = data.controls.get(controls::draft::SensorTimestamp);
+	RPiController::Metadata lastMetadata;
 	Span<uint8_t> embeddedBuffer;
 
-	rpiMetadata_.Clear();
-
+	lastMetadata = std::move(rpiMetadata_);
 	fillDeviceStatus(data.controls);
 
 	if (data.embeddedBufferPresent) {
@@ -920,6 +936,32 @@ void IPARPi::prepareISP(const ipa::RPi::ISPConfig &data)
 	if (data.embeddedBufferPresent)
 		returnEmbeddedBuffer(data.embeddedBufferId);
 
+	if (lastRunTimestamp_ && frameCount_ > dropFrameCount_ &&
+	    frameTimestamp - lastRunTimestamp_ < controllerMinFrameDuration * 1e3) {
+		/*
+		 * Ensure we update the controller metadata with the new frame's
+		 * exposure/gain values so that the correct values are returned
+		 * out in libcamera metadata later on. Any other bits of metadata
+		 * that were added in helper_->Prepare() will also be moved across.
+		 * All other metadata values must remain the same as the last frame.
+		 *
+		 * We do this by merging the current frame's metadata into the
+		 * previous frame's metadata object, and then moving the latter
+		 * into the former.
+		 */
+		lastMetadata.Merge(rpiMetadata_);
+		rpiMetadata_ = std::move(lastMetadata);
+		processPending_ = false;
+		LOG(IPARPI, Debug) << "Rate-limiting the controller! inter-frame duration: "
+				   << frameTimestamp - lastRunTimestamp_
+				   << ", min duration: "
+				   << controllerMinFrameDuration * 1e3;
+		return;
+	}
+
+	lastRunTimestamp_ = frameTimestamp;
+	processPending_ = true;
+
 	ControlList ctrls(ispCtrls_);
 
 	controller_.Prepare(&rpiMetadata_);
diff --git a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
index 2a917455500f..9cf9c8c6cebd 100644
--- a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
+++ b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
@@ -1414,6 +1414,11 @@ void RPiCameraData::unicamBufferDequeue(FrameBuffer *buffer)
 		 * DelayedControl and queue them along with the frame buffer.
 		 */
 		ControlList ctrl = delayedCtrls_->get(buffer->metadata().sequence);
+		/*
+		 * Add the frame timestamp to the ControlList for the IPA to use
+		 * as it does not receive the FrameBuffer object.
+		 */
+		ctrl.set(controls::draft::SensorTimestamp, buffer->metadata().timestamp);
 		bayerQueue_.push({ buffer, std::move(ctrl) });
 	} else {
 		embeddedQueue_.push(buffer);
-- 
2.25.1