[PATCH v2 2/3] ipa: libipa: agc_mean_luminance: Error out when effectiveExposureValue is zero

[Laurent Pinchart]

Hi Stefan,

Thank you for the patch.

On Wed, Mar 26, 2025 at 02:47:21PM +0100, Stefan Klug wrote:
> 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>
> Reviewed-by: Daniel Scally <dan.scally at ideasonboard.com>

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> ---
> 
> Changes in v2:
> - Collected tags
> - Improved log message wording
> - Added comment on the arbitrary exposure time
> ---
>  src/ipa/libipa/agc_mean_luminance.cpp | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/src/ipa/libipa/agc_mean_luminance.cpp b/src/ipa/libipa/agc_mean_luminance.cpp
> index 02555a44d271..f617fde81101 100644
> --- a/src/ipa/libipa/agc_mean_luminance.cpp
> +++ b/src/ipa/libipa/agc_mean_luminance.cpp
> @@ -541,6 +541,18 @@ AgcMeanLuminance::calculateNewEv(uint32_t constraintModeIndex,
>  	std::shared_ptr<ExposureModeHelper> exposureModeHelper =
>  		exposureModeHelpers_.at(exposureModeIndex);
>  
> +	if (effectiveExposureValue == 0s) {
> +		LOG(AgcMeanLuminance, Error)
> +			<< "Effective exposure value is 0. This is a bug in AGC "
> +			   "and must be fixed for proper operation.";
> +		/*
> +		 * Return an arbitrary exposure time > 0 to ensure regulation
> +		 * doesn't get stuck with 0 in case the sensor driver allows a
> +		 * min exposure of 0.
> +		 */
> +		return exposureModeHelper->splitExposure(10ms);
> +	}
> +
>  	double gain = estimateInitialGain();
>  	gain = constraintClampGain(constraintModeIndex, yHist, gain);
>  

-- 
Regards,

Laurent Pinchart