ipa: ipu3: agc: Introduce previous exposure value

We need to calculate the gain on the previous exposure value calculated.
Now that we initialise the exposure and gain values in configure(), we
know the initial exposure value, and we can set it before any loop is
running.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/ipa/ipu3/algorithms/agc.cpp

@@ -42,7 +42,8 @@ static constexpr double kEvGainTarget = 0.5;
 Agc::Agc()
 	: frameCount_(0), lastFrame_(0), iqMean_(0.0), lineDuration_(0s),
 	  minExposureLines_(0), maxExposureLines_(0), filteredExposure_(0s),
-	  filteredExposureNoDg_(0s), currentExposure_(0s), currentExposureNoDg_(0s)
+	  filteredExposureNoDg_(0s), currentExposure_(0s),
+	  currentExposureNoDg_(0s), prevExposureValue_(0s)
 {
 }
 
@@ -62,6 +63,10 @@ int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
 		context.configuration.agc.minAnalogueGain;
 	context.frameContext.agc.exposure = minExposureLines_;
 
+	prevExposureValue_ = context.frameContext.agc.gain
+			   * context.frameContext.agc.exposure
+			   * lineDuration_;
+
 	return 0;
 }
 
@@ -147,7 +152,7 @@ void Agc::lockExposureGain(uint32_t &exposure, double &analogueGain)
 				    << " Gain " << analogueGain
 				    << " Needed ev gain " << evGain;
 
-		currentExposure_ = currentExposureNoDg_ * evGain;
+		currentExposure_ = prevExposureValue_ * evGain;
 		utils::Duration minShutterSpeed = minExposureLines_ * lineDuration_;
 		utils::Duration maxShutterSpeed = maxExposureLines_ * lineDuration_;
 
@@ -176,6 +181,16 @@ void Agc::lockExposureGain(uint32_t &exposure, double &analogueGain)
 
 		exposure = shutterTime / lineDuration_;
 		analogueGain = stepGain;
+
+		/*
+		 * Update the exposure value for the next process call.
+		 *
+		 * \todo Obtain the values of the exposure time and analog gain
+		 * that were actually used by the sensor, either from embedded
+		 * data when available, or from the delayed controls
+		 * infrastructure in case a slow down caused a mismatch.
+		 */
+		prevExposureValue_ = shutterTime * analogueGain;
 	}
 	lastFrame_ = frameCount_;
 }

src/ipa/ipu3/algorithms/agc.h

@@ -49,6 +49,7 @@ private:
 	utils::Duration filteredExposureNoDg_;
 	utils::Duration currentExposure_;
 	utils::Duration currentExposureNoDg_;
+	utils::Duration prevExposureValue_;
 
 	uint32_t stride_;
 };