[PATCH 2/3] ipa: libipa: agc_mean_luminance: Error out when effectiveExposureValue is zero

[Stefan Klug]

In a proper system it never happens that the effectiveExposureValue
drops to zero. If that still happens due to a bug outside of
agc_mean_luminance, the calculated gain goes towards infinity but the
newExposureValue is still 0 because it is the result of multiplying the
effectiveExposureTime with the gain, leading to wild oscillations.

Catch that condition, print an error message and set the new effective
exposure value to an arbitrary 10ms.

Note that in any case the underlying problem must be fixed. The
important change is the added error message to be able to detect such a
situation.

Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
---
 src/ipa/libipa/agc_mean_luminance.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/ipa/libipa/agc_mean_luminance.cpp b/src/ipa/libipa/agc_mean_luminance.cpp
index 02555a44d271..a7343c18f5aa 100644
--- a/src/ipa/libipa/agc_mean_luminance.cpp
+++ b/src/ipa/libipa/agc_mean_luminance.cpp
@@ -541,6 +541,13 @@ AgcMeanLuminance::calculateNewEv(uint32_t constraintModeIndex,
 	std::shared_ptr<ExposureModeHelper> exposureModeHelper =
 		exposureModeHelpers_.at(exposureModeIndex);
 
+	if (effectiveExposureValue == 0s) {
+		LOG(AgcMeanLuminance, Error) << "Effective exposure value is 0."
+					     << " Resetting exposure time and"
+					     << " gain to arbitrary defaults.";
+		return exposureModeHelper->splitExposure(10ms);
+	}
+
 	double gain = estimateInitialGain();
 	gain = constraintClampGain(constraintModeIndex, yHist, gain);
 
-- 
2.43.0