[libcamera-devel] [PATCH] ipa: ipu3: agc: Fix -nan exception

[Kate Hsuan]

The user may equip a cam cover to make sure security.If they want to
disable the cam, the cam cover could be physically closed to ensure
the image will not be delivered. In this situation, the image will be
all black and it triggers the -nan exception for some values.
Eventually, the exposure will be locked. As a result, we only can get
a black image.

evGain is calculated by kEvGainTarget * knumHistogramBins / iqMean_.
For a black image, a -nan of iqMean_ will lead evGain miss calculated.
Consequently, the exposure value can not be correctly estimated and be
locked at -nan as well. In this situation, evGain is set to 1.0 and try
to estimate again through the next frame. Also, an additional check
makes sure the exposure value is between minTotalExposure and
maxTotalExposure.

Signed-off-by: Kate Hsuan <hpa at redhat.com>
---
 src/ipa/ipu3/algorithms/agc.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
index b5d736c1..d965febe 100644
--- a/src/ipa/ipu3/algorithms/agc.cpp
+++ b/src/ipa/ipu3/algorithms/agc.cpp
@@ -191,6 +191,8 @@ void Agc::computeExposure(uint32_t &exposure, double &analogueGain)
 
 	/* Estimate the gain needed to have the proportion wanted */
 	double evGain = kEvGainTarget * knumHistogramBins / iqMean_;
+	if(std::isnan(evGain))
+		evGain = 1.0;
 
 	/* extracted from Rpi::Agc::computeTargetExposure */
 	/* Calculate the shutter time in seconds */
@@ -210,7 +212,9 @@ void Agc::computeExposure(uint32_t &exposure, double &analogueGain)
 
 	/* Clamp the exposure value to the min and max authorized */
 	utils::Duration maxTotalExposure = maxShutterSpeed * maxAnalogueGain_;
-	currentExposure_ = std::min(currentExposure_, maxTotalExposure);
+	utils::Duration minTotalExposure = minShutterSpeed * minAnalogueGain_;
+
+	currentExposure_ = std::clamp<utils::Duration>(currentExposure_, minTotalExposure, maxTotalExposure);
 	LOG(IPU3Agc, Debug) << "Target total exposure " << currentExposure_
 			    << ", maximum is " << maxTotalExposure;
 
@@ -232,7 +236,6 @@ void Agc::computeExposure(uint32_t &exposure, double &analogueGain)
 	LOG(IPU3Agc, Debug) << "Divided up shutter and gain are "
 			    << shutterTime << " and "
 			    << stepGain;
-
 	exposure = shutterTime / lineDuration_;
 	analogueGain = stepGain;
 
-- 
2.31.1