[libcamera-devel] [PATCH v1 1/2] ipa: raspberrypi: Limit the maximum sensor gain used

[Naushir Patuck]

Limit the gain code to the maximum value reported by the sensor controls when
sending to DelayedControls. The AGC algorithm will handle a lower gain used by
the sensor, provided provided it knows the actual gain used. This change ensures
that DelayedControls will never report an unclipped gain used.

Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
---
 src/ipa/raspberrypi/raspberrypi.cpp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/ipa/raspberrypi/raspberrypi.cpp b/src/ipa/raspberrypi/raspberrypi.cpp
index 0ed41385018a..a72d516f84ee 100644
--- a/src/ipa/raspberrypi/raspberrypi.cpp
+++ b/src/ipa/raspberrypi/raspberrypi.cpp
@@ -173,6 +173,9 @@ private:
 	/* Frame duration (1/fps) limits. */
 	Duration minFrameDuration_;
 	Duration maxFrameDuration_;
+
+	/* Maximum gain code for the sensor. */
+	uint32_t maxSensorGainCode_;
 };
 
 int IPARPi::init(const IPASettings &settings, ipa::RPi::SensorConfig *sensorConfig)
@@ -357,6 +360,8 @@ int IPARPi::configure(const IPACameraSensorInfo &sensorInfo,
 		return -1;
 	}
 
+	maxSensorGainCode_ = sensorCtrls_.at(V4L2_CID_ANALOGUE_GAIN).max().get<int32_t>();
+
 	/* Setup a metadata ControlList to output metadata. */
 	libcameraMetadata_ = ControlList(controls::controls);
 
@@ -1113,6 +1118,13 @@ void IPARPi::applyAGC(const struct AgcStatus *agcStatus, ControlList &ctrls)
 {
 	int32_t gainCode = helper_->GainCode(agcStatus->analogue_gain);
 
+	/*
+	 * Ensure anything larger than the max gain code will not be passed to
+	 * DelayedControls. The AGC will correctly handle a lower gain returned
+	 * by the sensor, provided it knows the actual gain used.
+	 */
+	gainCode = std::min<int32_t>(gainCode, maxSensorGainCode_);
+
 	/* GetVBlanking might clip exposure time to the fps limits. */
 	Duration exposure = agcStatus->shutter_time;
 	int32_t vblanking = helper_->GetVBlanking(exposure, minFrameDuration_, maxFrameDuration_);
-- 
2.25.1