[libcamera-devel] [PATCH v3 3/3] libcamera: pipeline: raspberrypi: Update sensor's V4L2_CID_NOTIFY_GAINS control

[David Plowman]

If the sensor exposes the V4L2_CID_NOTIFY_GAINS control, assume it
means the sensor wants to be told the latest colour gains.

We store whether the control exists and if so its default value, to
save us checking for it on every frame.

Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
---
 .../pipeline/raspberrypi/raspberrypi.cpp      | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
index b5c687da..4adef952 100644
--- a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
+++ b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
@@ -264,6 +264,12 @@ public:
 
 	unsigned int dropFrameCount_;
 
+	/*
+	 * If set, this stores the value that represets a gain of one for
+	 * the V4L2_CID_NOTIFY_GAINS control.
+	 */
+	std::optional<int32_t> notifyGainsUnity_;
+
 private:
 	void checkRequestCompleted();
 	void fillRequestMetadata(const ControlList &bufferControls,
@@ -1191,6 +1197,15 @@ int PipelineHandlerRPi::registerCamera(MediaDevice *unicam, MediaDevice *isp)
 	/* Initialize the camera properties. */
 	data->properties_ = data->sensor_->properties();
 
+	/*
+	 * The V4L2_CID_NOTIFY_GAINS control, if present, is used to inform the
+	 * sensor of the colour gains. It is defined to be a linear gain where
+	 * the default value represents a gain of exactly one.
+	 */
+	auto it = data->sensor_->controls().find(V4L2_CID_NOTIFY_GAINS);
+	if (it != data->sensor_->controls().end())
+		data->notifyGainsUnity_ = it->second.def().get<int32_t>();
+
 	/*
 	 * Set a default value for the ScalerCropMaximum property to show
 	 * that we support its use, however, initialise it to zero because
@@ -1495,6 +1510,22 @@ void RPiCameraData::statsMetadataComplete(uint32_t bufferId, const ControlList &
 	Request *request = requestQueue_.front();
 	request->metadata().merge(controls);
 
+	/*
+	 * Inform the sensor of the latest colour gains if it has the
+	 * V4L2_CID_NOTIFY_GAINS control (which means notifyGainsUnity_ is set).
+	 */
+	if (notifyGainsUnity_ && controls.contains(libcamera::controls::ColourGains)) {
+		libcamera::Span<const float> colourGains = controls.get(libcamera::controls::ColourGains);
+		/* The control wants linear gains in the order B, Gb, Gr, R. */
+		ControlList ctrls(sensor_->controls());
+		std::array<int32_t, 4> gains = { static_cast<int32_t>(colourGains[1] * *notifyGainsUnity_),
+						 *notifyGainsUnity_, *notifyGainsUnity_,
+						 static_cast<int32_t>(colourGains[0] * *notifyGainsUnity_) };
+		ctrls.set(V4L2_CID_NOTIFY_GAINS, Span<const int32_t>{ gains });
+
+		sensor_->setControls(&ctrls);
+	}
+
 	state_ = State::IpaComplete;
 	handleState();
 }
-- 
2.30.2