[libcamera-devel] [PATCH v2 3/4] ipa: raspberrypi: Ensure shutter speed and gain are clipped in the AGC

[Naushir Patuck]

Make a copy of the CameraMode structure on a switch mode call. This
replaces the existing lastSensitivity_ field.

Limit the AGC gain calculations to the minimum value given by the
CameraMode structure. The maximum value remains unclipped as any gain
over the sensor maximum will be made up by digital gain.

Rename clipShutter to limitShutter for consistency, and have the latter
limit the shutter speed to both upper and lower bounds.

Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
---
 src/ipa/raspberrypi/controller/rpi/agc.cpp | 55 +++++++++++++++++-----
 src/ipa/raspberrypi/controller/rpi/agc.h   |  4 +-
 2 files changed, 45 insertions(+), 14 deletions(-)

diff --git a/src/ipa/raspberrypi/controller/rpi/agc.cpp b/src/ipa/raspberrypi/controller/rpi/agc.cpp
index 4ea0dd41e66c..ed7ecbe05a8e 100644
--- a/src/ipa/raspberrypi/controller/rpi/agc.cpp
+++ b/src/ipa/raspberrypi/controller/rpi/agc.cpp
@@ -309,14 +309,14 @@ void Agc::setFixedShutter(Duration fixedShutter)
 {
 	fixedShutter_ = fixedShutter;
 	/* Set this in case someone calls disableAuto() straight after. */
-	status_.shutterTime = clipShutter(fixedShutter_);
+	status_.shutterTime = limitShutter(fixedShutter_);
 }
 
 void Agc::setFixedAnalogueGain(double fixedAnalogueGain)
 {
 	fixedAnalogueGain_ = fixedAnalogueGain;
 	/* Set this in case someone calls disableAuto() straight after. */
-	status_.analogueGain = fixedAnalogueGain;
+	status_.analogueGain = limitGain(fixedAnalogueGain);
 }
 
 void Agc::setMeteringMode(std::string const &meteringModeName)
@@ -342,7 +342,7 @@ void Agc::switchMode(CameraMode const &cameraMode,
 
 	housekeepConfig();
 
-	Duration fixedShutter = clipShutter(fixedShutter_);
+	Duration fixedShutter = limitShutter(fixedShutter_);
 	if (fixedShutter && fixedAnalogueGain_) {
 		/* We're going to reset the algorithm here with these fixed values. */
 
@@ -371,7 +371,7 @@ void Agc::switchMode(CameraMode const &cameraMode,
 		 * current exposure profile, which takes care of everything else.
 		 */
 
-		double ratio = lastSensitivity_ / cameraMode.sensitivity;
+		double ratio = mode_.sensitivity / cameraMode.sensitivity;
 		target_.totalExposureNoDG *= ratio;
 		target_.totalExposure *= ratio;
 		filtered_.totalExposureNoDG *= ratio;
@@ -393,8 +393,11 @@ void Agc::switchMode(CameraMode const &cameraMode,
 
 	writeAndFinish(metadata, false);
 
-	/* We must remember the sensitivity of this mode for the next SwitchMode. */
-	lastSensitivity_ = cameraMode.sensitivity;
+	/*
+	 * Store the more in the local state. We must remember the sensitivity
+	 * of this mode for the next SwitchMode.
+	 */
+	mode_ = cameraMode;
 }
 
 void Agc::prepare(Metadata *imageMetadata)
@@ -516,7 +519,7 @@ void Agc::housekeepConfig()
 {
 	/* First fetch all the up-to-date settings, so no one else has to do it. */
 	status_.ev = ev_;
-	status_.fixedShutter = clipShutter(fixedShutter_);
+	status_.fixedShutter = limitShutter(fixedShutter_);
 	status_.fixedAnalogueGain = fixedAnalogueGain_;
 	status_.flickerPeriod = flickerPeriod_;
 	LOG(RPiAgc, Debug) << "ev " << status_.ev << " fixedShutter "
@@ -703,7 +706,7 @@ void Agc::computeTargetExposure(double gain)
 		Duration maxShutter = status_.fixedShutter
 					      ? status_.fixedShutter
 					      : exposureMode_->shutter.back();
-		maxShutter = clipShutter(maxShutter);
+		maxShutter = limitShutter(maxShutter);
 		Duration maxTotalExposure =
 			maxShutter *
 			(status_.fixedAnalogueGain != 0.0
@@ -803,15 +806,16 @@ void Agc::divideUpExposure()
 	double analogueGain;
 	shutterTime = status_.fixedShutter ? status_.fixedShutter
 					   : exposureMode_->shutter[0];
-	shutterTime = clipShutter(shutterTime);
+	shutterTime = limitShutter(shutterTime);
 	analogueGain = status_.fixedAnalogueGain != 0.0 ? status_.fixedAnalogueGain
 							: exposureMode_->gain[0];
+	analogueGain = limitGain(analogueGain);
 	if (shutterTime * analogueGain < exposureValue) {
 		for (unsigned int stage = 1;
 		     stage < exposureMode_->gain.size(); stage++) {
 			if (!status_.fixedShutter) {
 				Duration stageShutter =
-					clipShutter(exposureMode_->shutter[stage]);
+					limitShutter(exposureMode_->shutter[stage]);
 				if (stageShutter * analogueGain >= exposureValue) {
 					shutterTime = exposureValue / analogueGain;
 					break;
@@ -824,6 +828,7 @@ void Agc::divideUpExposure()
 					break;
 				}
 				analogueGain = exposureMode_->gain[stage];
+				analogueGain = limitGain(analogueGain);
 			}
 		}
 	}
@@ -846,6 +851,7 @@ void Agc::divideUpExposure()
 			 * gain as a side-effect.
 			 */
 			analogueGain = std::min(analogueGain, exposureMode_->gain.back());
+			analogueGain = limitGain(analogueGain);
 			shutterTime = newShutterTime;
 		}
 		LOG(RPiAgc, Debug) << "After flicker avoidance, shutter "
@@ -872,13 +878,36 @@ void Agc::writeAndFinish(Metadata *imageMetadata, bool desaturate)
 			   << " analogue gain " << filtered_.analogueGain;
 }
 
-Duration Agc::clipShutter(Duration shutter)
+Duration Agc::limitShutter(Duration shutter)
 {
-	if (maxShutter_)
-		shutter = std::min(shutter, maxShutter_);
+	/*
+	 * shutter == 0 is a special case for fixed shutter values, and must pass
+	 * through unchanged
+	 */
+	if (!shutter)
+		return shutter;
+
+	shutter = std::clamp(shutter, mode_.minShutter, maxShutter_);
 	return shutter;
 }
 
+double Agc::limitGain(double gain) const
+{
+	/*
+	 * Only limit the lower bounds of the gain value to what the sensor limits.
+	 * The upper bound on analogue gain will be made up with additional digital
+	 * gain applied by the ISP.
+	 *
+	 * gain == 0.0 is a special case for fixed shutter values, and must pass
+	 * through unchanged
+	 */
+	if (!gain)
+		return gain;
+
+	gain = std::max(gain, mode_.minAnalogueGain);
+	return gain;
+}
+
 /* Register algorithm with the system. */
 static Algorithm *create(Controller *controller)
 {
diff --git a/src/ipa/raspberrypi/controller/rpi/agc.h b/src/ipa/raspberrypi/controller/rpi/agc.h
index f04896ca25ad..661d8b08cea2 100644
--- a/src/ipa/raspberrypi/controller/rpi/agc.h
+++ b/src/ipa/raspberrypi/controller/rpi/agc.h
@@ -103,10 +103,12 @@ private:
 	void filterExposure(bool desaturate);
 	void divideUpExposure();
 	void writeAndFinish(Metadata *imageMetadata, bool desaturate);
-	libcamera::utils::Duration clipShutter(libcamera::utils::Duration shutter);
+	libcamera::utils::Duration limitShutter(libcamera::utils::Duration shutter);
+	double limitGain(double gain) const;
 	AgcMeteringMode *meteringMode_;
 	AgcExposureMode *exposureMode_;
 	AgcConstraintMode *constraintMode_;
+	CameraMode mode_;
 	uint64_t frameCount_;
 	AwbStatus awb_;
 	struct ExposureValues {
-- 
2.34.1