ipa: raspberrypi: agc: Add GetConvergenceFrames method to AGC base class

We add a GetConvergenceFrames method to the AgcAlgorithm class which
can be called when the AGC is started from scratch. It suggests how
many frames should be dropped before displaying any (while the AGC
converges).

The Raspberry Pi specific implementation makes this customisable from
the tuning file.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/ipa/raspberrypi/controller/rpi/agc.cpp

@@ -142,6 +142,7 @@ void AgcConfig::Read(boost::property_tree::ptree const &params)
 	Y_target.Read(params.get_child("y_target"));
 	speed = params.get<double>("speed", 0.2);
 	startup_frames = params.get<uint16_t>("startup_frames", 10);
+	convergence_frames = params.get<unsigned int>("convergence_frames", 6);
 	fast_reduce_threshold =
 		params.get<double>("fast_reduce_threshold", 0.4);
 	base_ev = params.get<double>("base_ev", 1.0);
@@ -206,6 +207,16 @@ void Agc::Resume()
 	fixed_analogue_gain_ = 0;
 }
 
+unsigned int Agc::GetConvergenceFrames() const
+{
+	// If shutter and gain have been explicitly set, there is no
+	// convergence to happen, so no need to drop any frames - return zero.
+	if (fixed_shutter_ && fixed_analogue_gain_)
+		return 0;
+	else
+		return config_.convergence_frames;
+}
+
 void Agc::SetEv(double ev)
 {
 	ev_ = ev;