From 8896ca13f1dee770dde2d9e8adfcf4ec00f65f5b Mon Sep 17 00:00:00 2001
From: Kieran Bingham <kieran.bingham@ideasonboard.com>
Date: Thu, 19 Feb 2026 15:05:14 +0000
Subject: [PATCH] ipa: mali-c55: agc: Quantise the ISP Digital Gain

The Mali-C55 ISP has a digital gain block which allows setting gain in Q5.8
format, a range of 0.0 to (very nearly) 32.0.

Convert usage to the new UQ<5, 8> FixedPoint Quantised type which will
support the conversion, clamping and quantisation so that the metadata
and debug prints can now report the effective gain applied instead of
the potentially inaccurate float.

Reviewed-by: Isaac Scott <isaac.scott@ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
---
 src/ipa/mali-c55/algorithms/agc.cpp | 25 ++++++++++++-------------
 src/ipa/mali-c55/ipa_context.h      |  6 +++---
 2 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/src/ipa/mali-c55/algorithms/agc.cpp b/src/ipa/mali-c55/algorithms/agc.cpp
index 014fd124..34d67667 100644
--- a/src/ipa/mali-c55/algorithms/agc.cpp
+++ b/src/ipa/mali-c55/algorithms/agc.cpp
@@ -38,8 +38,8 @@ static constexpr unsigned int kNumHistogramBins = 256;
  * format, a range of 0.0 to (very nearly) 32.0. We clamp from 1.0 to the actual
  * max value which is 8191 * 2^-8.
  */
-static constexpr double kMinDigitalGain = 1.0;
-static constexpr double kMaxDigitalGain = 31.99609375;
+static constexpr float kMinDigitalGain = 1.0;
+static constexpr float kMaxDigitalGain = UQ<5, 8>::TraitsType::max;
 
 uint32_t AgcStatistics::decodeBinValue(uint16_t binVal)
 {
@@ -139,10 +139,7 @@ int Agc::init(IPAContext &context, const YamlObject &tuningData)
 
 	context.ctrlMap[&controls::AeEnable] = ControlInfo(false, true);
 	context.ctrlMap[&controls::DigitalGain] = ControlInfo(
-		static_cast<float>(kMinDigitalGain),
-		static_cast<float>(kMaxDigitalGain),
-		static_cast<float>(kMinDigitalGain)
-	);
+		kMinDigitalGain, kMaxDigitalGain, kMinDigitalGain);
 	context.ctrlMap.merge(controls());
 
 	return 0;
@@ -245,7 +242,7 @@ void Agc::fillGainParamBlock(IPAContext &context, IPAFrameContext &frameContext,
 			     MaliC55Params *params)
 {
 	IPAActiveState &activeState = context.activeState;
-	double gain;
+	UQ<5, 8> gain;
 
 	if (activeState.agc.autoEnabled)
 		gain = activeState.agc.automatic.ispGain;
@@ -253,7 +250,7 @@ void Agc::fillGainParamBlock(IPAContext &context, IPAFrameContext &frameContext,
 		gain = activeState.agc.manual.ispGain;
 
 	auto block = params->block<MaliC55Blocks::Dgain>();
-	block->gain = floatingToFixedPoint<5, 8, uint16_t, double>(gain);
+	block->gain = gain.quantized();
 
 	frameContext.agc.ispGain = gain;
 }
@@ -358,7 +355,7 @@ void Agc::process(IPAContext &context,
 	 */
 	uint32_t exposure = frameContext.agc.exposure;
 	double analogueGain = frameContext.agc.sensorGain;
-	double digitalGain = frameContext.agc.ispGain;
+	double digitalGain = frameContext.agc.ispGain.value();
 	double totalGain = analogueGain * digitalGain;
 	utils::Duration currentShutter = exposure * configuration.sensor.lineDuration;
 	utils::Duration effectiveExposureValue = currentShutter * totalGain;
@@ -370,19 +367,21 @@ void Agc::process(IPAContext &context,
 			       activeState.agc.exposureMode, statistics_.yHist,
 			       effectiveExposureValue);
 
-	dGain = std::clamp(dGain, kMinDigitalGain, kMaxDigitalGain);
+	UQ<5, 8> dGainQ = std::clamp(static_cast<float>(dGain),
+				     kMinDigitalGain,
+				     kMaxDigitalGain);
 
 	LOG(MaliC55Agc, Debug)
 		<< "Divided up shutter, analogue gain and digital gain are "
-		<< shutterTime << ", " << aGain << " and " << dGain;
+		<< shutterTime << ", " << aGain << " and " << dGainQ;
 
 	activeState.agc.automatic.exposure = shutterTime / configuration.sensor.lineDuration;
 	activeState.agc.automatic.sensorGain = aGain;
-	activeState.agc.automatic.ispGain = dGain;
+	activeState.agc.automatic.ispGain = dGainQ;
 
 	metadata.set(controls::ExposureTime, currentShutter.get<std::micro>());
 	metadata.set(controls::AnalogueGain, frameContext.agc.sensorGain);
-	metadata.set(controls::DigitalGain, frameContext.agc.ispGain);
+	metadata.set(controls::DigitalGain, frameContext.agc.ispGain.value());
 	metadata.set(controls::ColourTemperature, context.activeState.agc.temperatureK);
 }
 
diff --git a/src/ipa/mali-c55/ipa_context.h b/src/ipa/mali-c55/ipa_context.h
index 08f78e4f..ac4b8377 100644
--- a/src/ipa/mali-c55/ipa_context.h
+++ b/src/ipa/mali-c55/ipa_context.h
@@ -41,12 +41,12 @@ struct IPAActiveState {
 		struct {
 			uint32_t exposure;
 			double sensorGain;
-			double ispGain;
+			UQ<5, 8> ispGain;
 		} automatic;
 		struct {
 			uint32_t exposure;
 			double sensorGain;
-			double ispGain;
+			UQ<5, 8> ispGain;
 		} manual;
 		bool autoEnabled;
 		uint32_t constraintMode;
@@ -64,7 +64,7 @@ struct IPAFrameContext : public FrameContext {
 	struct {
 		uint32_t exposure;
 		double sensorGain;
-		double ispGain;
+		UQ<5, 8> ispGain;
 	} agc;
 
 	struct {