[PATCH v2 1/4] ipa: rkisp1: agc: Use better defaults for analogue gain and exposure

[Mikhail Rudenko]

At present, analogue gain in IPA context is initialized to the minimum
sensor gain in configure(). Many sensors report minimum analogue gain
of 0, which is by no means a sane default. Use a reasonable default of
1.0 instead. Also, set default exposure to maximum. In the common case
when no gain stages are configured and no gain/exposure constraints
are set, these defaults result in having right gain or exposure from
the start, since AGC either sets 1.0 gain and steers exposure (lighter
scenes), or sets max exposure and steers gain (darker scenes).

Signed-off-by: Mikhail Rudenko <mike.rudenko at gmail.com>
---
 src/ipa/rkisp1/algorithms/agc.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/ipa/rkisp1/algorithms/agc.cpp b/src/ipa/rkisp1/algorithms/agc.cpp
index 17d074d9..2b36d7aa 100644
--- a/src/ipa/rkisp1/algorithms/agc.cpp
+++ b/src/ipa/rkisp1/algorithms/agc.cpp
@@ -30,9 +30,12 @@
 namespace libcamera {
 
 using namespace std::literals::chrono_literals;
+using utils::Duration;
 
 namespace ipa::rkisp1::algorithms {
 
+constexpr double defaultAnalogueGain = 1.0;
+
 /**
  * \class Agc
  * \brief A mean-based auto-exposure algorithm
@@ -164,9 +167,9 @@ int Agc::init(IPAContext &context, const YamlObject &tuningData)
 int Agc::configure(IPAContext &context, const IPACameraSensorInfo &configInfo)
 {
 	/* Configure the default exposure and gain. */
-	context.activeState.agc.automatic.gain = context.configuration.sensor.minAnalogueGain;
+	context.activeState.agc.automatic.gain = defaultAnalogueGain;
 	context.activeState.agc.automatic.exposure =
-		10ms / context.configuration.sensor.lineDuration;
+		context.configuration.sensor.maxShutterSpeed / context.configuration.sensor.lineDuration;
 	context.activeState.agc.manual.gain = context.activeState.agc.automatic.gain;
 	context.activeState.agc.manual.exposure = context.activeState.agc.automatic.exposure;
 	context.activeState.agc.autoEnabled = !context.configuration.raw;
-- 
2.46.0