[libcamera-devel] [PATCH v2 3/3] ipa: ipu3: agc: Introduce lineDuration in IPASessionConfiguration

[Jean-Michel Hautbois]

Instead of having a local cached value for line duration, store it in
the IPASessionConfiguration::agc structure.
While at it, configure the default analogue gain and shutter speed to
controlled fixed values.

The latter is set to be 10ms as it will in most cases be close to the
one needed, making the AGC faster to converge.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
---
 src/ipa/ipu3/algorithms/agc.cpp | 25 +++++++++++++++----------
 src/ipa/ipu3/algorithms/agc.h   |  3 +--
 src/ipa/ipu3/ipa_context.cpp    |  3 +++
 src/ipa/ipu3/ipa_context.h      |  1 +
 4 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
index a929085c..137c36cf 100644
--- a/src/ipa/ipu3/algorithms/agc.cpp
+++ b/src/ipa/ipu3/algorithms/agc.cpp
@@ -71,7 +71,7 @@ static constexpr uint32_t kNumStartupFrames = 10;
 static constexpr double kRelativeLuminanceTarget = 0.16;
 
 Agc::Agc()
-	: frameCount_(0), lineDuration_(0s), minShutterSpeed_(0s),
+	: frameCount_(0), minShutterSpeed_(0s),
 	  maxShutterSpeed_(0s), filteredExposure_(0s)
 {
 }
@@ -85,11 +85,14 @@ Agc::Agc()
  */
 int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
 {
-	stride_ = context.configuration.grid.stride;
+	IPASessionConfiguration &configuration = context.configuration;
+	IPAFrameContext &frameContext = context.frameContext;
+
+	stride_ = configuration.grid.stride;
 
 	/* \todo use the IPAContext to provide the limits */
-	lineDuration_ = configInfo.sensorInfo.lineLength * 1.0s
-		      / configInfo.sensorInfo.pixelRate;
+	configuration.agc.lineDuration = configInfo.sensorInfo.lineLength * 1.0s
+				       / configInfo.sensorInfo.pixelRate;
 
 	minShutterSpeed_ = context.configuration.agc.minShutterSpeed;
 	maxShutterSpeed_ = std::min(context.configuration.agc.maxShutterSpeed,
@@ -99,8 +102,8 @@ int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
 	maxAnalogueGain_ = std::min(context.configuration.agc.maxAnalogueGain, kMaxAnalogueGain);
 
 	/* Configure the default exposure and gain. */
-	context.frameContext.agc.gain = minAnalogueGain_;
-	context.frameContext.agc.exposure = minShutterSpeed_ / lineDuration_;
+	frameContext.agc.gain = std::max(minAnalogueGain_, kMinAnalogueGain);
+	frameContext.agc.exposure = 10ms / configuration.agc.lineDuration;
 
 	return 0;
 }
@@ -182,9 +185,11 @@ utils::Duration Agc::filterExposure(utils::Duration exposureValue)
  * \param[in] yGain The gain calculated based on the relative luminance target
  * \param[in] iqMeanGain The gain calculated based on the relative luminance target
  */
-void Agc::computeExposure(IPAFrameContext &frameContext, double yGain,
+void Agc::computeExposure(IPAContext &context, double yGain,
 			  double iqMeanGain)
 {
+	const IPASessionConfiguration &configuration = context.configuration;
+	IPAFrameContext &frameContext = context.frameContext;
 	/* Get the effective exposure and gain applied on the sensor. */
 	uint32_t exposure = frameContext.sensor.exposure;
 	double analogueGain = frameContext.sensor.gain;
@@ -200,7 +205,7 @@ void Agc::computeExposure(IPAFrameContext &frameContext, double yGain,
 	/* extracted from Rpi::Agc::computeTargetExposure */
 
 	/* Calculate the shutter time in seconds */
-	utils::Duration currentShutter = exposure * lineDuration_;
+	utils::Duration currentShutter = exposure * configuration.agc.lineDuration;
 
 	/*
 	 * Update the exposure value for the next computation using the values
@@ -247,7 +252,7 @@ void Agc::computeExposure(IPAFrameContext &frameContext, double yGain,
 			    << stepGain;
 
 	/* Update the estimated exposure and gain. */
-	frameContext.agc.exposure = shutterTime / lineDuration_;
+	frameContext.agc.exposure = shutterTime / configuration.agc.lineDuration;
 	frameContext.agc.gain = stepGain;
 }
 
@@ -354,7 +359,7 @@ void Agc::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
 			break;
 	}
 
-	computeExposure(context.frameContext, yGain, iqMeanGain);
+	computeExposure(context, yGain, iqMeanGain);
 	frameCount_++;
 }
 
diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
index 84bfe045..ad705605 100644
--- a/src/ipa/ipu3/algorithms/agc.h
+++ b/src/ipa/ipu3/algorithms/agc.h
@@ -34,7 +34,7 @@ private:
 	double measureBrightness(const ipu3_uapi_stats_3a *stats,
 				 const ipu3_uapi_grid_config &grid) const;
 	utils::Duration filterExposure(utils::Duration currentExposure);
-	void computeExposure(IPAFrameContext &frameContext, double yGain,
+	void computeExposure(IPAContext &context, double yGain,
 			     double iqMeanGain);
 	double estimateLuminance(IPAFrameContext &frameContext,
 				 const ipu3_uapi_grid_config &grid,
@@ -43,7 +43,6 @@ private:
 
 	uint64_t frameCount_;
 
-	utils::Duration lineDuration_;
 	utils::Duration minShutterSpeed_;
 	utils::Duration maxShutterSpeed_;
 
diff --git a/src/ipa/ipu3/ipa_context.cpp b/src/ipa/ipu3/ipa_context.cpp
index 86794ac1..ace9c66f 100644
--- a/src/ipa/ipu3/ipa_context.cpp
+++ b/src/ipa/ipu3/ipa_context.cpp
@@ -84,6 +84,9 @@ namespace libcamera::ipa::ipu3 {
  *
  * \var IPASessionConfiguration::agc.maxAnalogueGain
  * \brief Maximum analogue gain supported with the configured sensor
+ *
+ * \var IPASessionConfiguration::agc.lineDuration
+ * \brief Line duration in microseconds
  */
 
 /**
diff --git a/src/ipa/ipu3/ipa_context.h b/src/ipa/ipu3/ipa_context.h
index c6dc0814..7696fd14 100644
--- a/src/ipa/ipu3/ipa_context.h
+++ b/src/ipa/ipu3/ipa_context.h
@@ -30,6 +30,7 @@ struct IPASessionConfiguration {
 		utils::Duration maxShutterSpeed;
 		double minAnalogueGain;
 		double maxAnalogueGain;
+		utils::Duration lineDuration;
 	} agc;
 };
 
-- 
2.32.0