[PATCH v6 1/2] ipa: rkisp1: agc: Read histogram weights from tuning file

[Paul Elder]

Add support to the rkisp1 AGC to read histogram weights from the tuning
file. As controls for selecting the metering mode are not yet supported,
for now hardcode the matrix metering mode, which is the same as what the
AGC previously hardcoded.

Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug at ideasonboard.com>
Reviewed-by: Daniel Scally <dan.scally at ideasonboard.com>

---
Changes in v6:
- fix predivider calculation
- misc cleanups
- remove support for v12 (technically it depends on what the tuning file
  provides)

No change in v5

Changes in v4:
- add debug print when parsing the yaml file

Changes in v3:
- support the new tuning file layout for interpolated matrices
- support both v10 and v12

Changes in v2:
- add default metering mode if none are read successfully from the
  tuning file
- compute the predivider instead of using a table
---
 src/ipa/rkisp1/algorithms/agc.cpp | 100 +++++++++++++++++++++++++++++-
 src/ipa/rkisp1/algorithms/agc.h   |   6 ++
 2 files changed, 103 insertions(+), 3 deletions(-)

diff --git a/src/ipa/rkisp1/algorithms/agc.cpp b/src/ipa/rkisp1/algorithms/agc.cpp
index 50e0690fe146..5a9c6be118d9 100644
--- a/src/ipa/rkisp1/algorithms/agc.cpp
+++ b/src/ipa/rkisp1/algorithms/agc.cpp
@@ -17,6 +17,8 @@
 #include <libcamera/control_ids.h>
 #include <libcamera/ipa/core_ipa_interface.h>
 
+#include "libcamera/internal/yaml_parser.h"
+
 #include "libipa/histogram.h"
 
 /**
@@ -36,6 +38,85 @@ namespace ipa::rkisp1::algorithms {
 
 LOG_DEFINE_CATEGORY(RkISP1Agc)
 
+int Agc::parseMeteringModes(IPAContext &context, const YamlObject &tuningData)
+{
+	if (!tuningData.isDictionary()) {
+		LOG(RkISP1Agc, Error)
+			<< "'AeMeteringMode' parameter not found in tuning file";
+		return -EINVAL;
+	}
+
+	for (const auto &[key, value] : tuningData.asDict()) {
+		if (controls::AeMeteringModeNameValueMap.find(key) ==
+		    controls::AeMeteringModeNameValueMap.end()) {
+			LOG(RkISP1Agc, Warning)
+				<< "Skipping unknown metering mode '" << key << "'";
+			continue;
+		}
+
+		std::vector<uint8_t> weights =
+			value.getList<uint8_t>().value_or(std::vector<uint8_t>{});
+		if (weights.size() != context.hw->numHistogramWeights) {
+			LOG(RkISP1Agc, Warning)
+				<< "Failed to read metering mode'" << key << "'";
+			continue;
+		}
+
+		meteringModes_[controls::AeMeteringModeNameValueMap.at(key)] = weights;
+	}
+
+	if (meteringModes_.empty()) {
+		LOG(RkISP1Agc, Warning)
+			<< "No metering modes read from tuning file; defaulting to matrix";
+		int32_t meteringModeId = controls::AeMeteringModeNameValueMap.at("MeteringMatrix");
+		std::vector<uint8_t> weights(context.hw->numHistogramWeights, 1);
+
+		meteringModes_[meteringModeId] = weights;
+	}
+
+	return 0;
+}
+
+uint8_t Agc::computeHistogramPredivider(Size &size, enum rkisp1_cif_isp_histogram_mode mode)
+{
+	/*
+	 * The maximum number of pixels that could potentially be in one bin is
+	 * if all the pixels of the image are in it, multiplied by 3 for the
+	 * three color channels. The counter for each bin is 16 bits wide, so
+	 * `factor` thus contains the number of times we'd wrap around. This is
+	 * obviously the number of pixels that we need to skip to make sure
+	 * that we don't wrap around, but we compute the square root of it
+	 * instead, as the skip that we need to program is for both the x and y
+	 * directions.
+	 *
+	 * Even though it looks like dividing into a counter of 65536 would
+	 * overflow by 1, this is apparently fine according to the hardware
+	 * documentation, and this successfully gets the expected documented
+	 * predivider size for cases where:
+	 * (width / predivider) * (height / predivider) * 3 == 65536.
+	 *
+	 * There's a bit of extra rounding math to make sure the rounding goes
+	 * the correct direction so that the square of the step is big enough
+	 * to encompass the `factor` number of pixels that we need to skip.
+	 *
+	 * \todo Take into account weights. That is, if the weights are low
+	 * enough we can potentially reduce the predivider to increase
+	 * precision. This needs some investigation however, as this hardware
+	 * behavior is undocumented and is only an educated guess.
+	 */
+	int count = mode == RKISP1_CIF_ISP_HISTOGRAM_MODE_RGB_COMBINED ? 3 : 1;
+	double factor = size.width * size.height * count / 65536.0;
+	double root = std::sqrt(factor);
+	uint8_t predivider;
+
+	if (std::pow(std::floor(root), 2) < factor)
+		predivider = static_cast<uint8_t>(std::ceil(root));
+	else
+		predivider = static_cast<uint8_t>(std::floor(root));
+
+	return std::clamp<uint8_t>(predivider, 3, 127);
+}
+
 Agc::Agc()
 {
 	supportsRaw_ = true;
@@ -59,6 +140,11 @@ int Agc::init(IPAContext &context, const YamlObject &tuningData)
 	if (ret)
 		return ret;
 
+	const YamlObject &yamlMeteringModes = tuningData["AeMeteringMode"];
+	ret = parseMeteringModes(context, yamlMeteringModes);
+	if (ret)
+		return ret;
+
 	context.ctrlMap.merge(controls());
 
 	return 0;
@@ -160,6 +246,7 @@ void Agc::prepare(IPAContext &context, const uint32_t frame,
 		frameContext.agc.gain = context.activeState.agc.automatic.gain;
 	}
 
+	/* \todo Remove this when we can set the below with controls */
 	if (frame > 0)
 		return;
 
@@ -178,14 +265,21 @@ void Agc::prepare(IPAContext &context, const uint32_t frame,
 	params->meas.hst_config.meas_window = context.configuration.agc.measureWindow;
 	/* Produce the luminance histogram. */
 	params->meas.hst_config.mode = RKISP1_CIF_ISP_HISTOGRAM_MODE_Y_HISTOGRAM;
+
 	/* Set an average weighted histogram. */
 	Span<uint8_t> weights{
 		params->meas.hst_config.hist_weight,
 		context.hw->numHistogramWeights
 	};
-	std::fill(weights.begin(), weights.end(), 1);
-	/* Step size can't be less than 3. */
-	params->meas.hst_config.histogram_predivider = 4;
+	/* \todo Get this from control */
+	std::vector<uint8_t> &modeWeights = meteringModes_.at(controls::MeteringMatrix);
+	std::copy(modeWeights.begin(), modeWeights.end(), weights.begin());
+
+	struct rkisp1_cif_isp_window window = params->meas.hst_config.meas_window;
+	Size windowSize = { window.h_size, window.v_size };
+	params->meas.hst_config.histogram_predivider =
+		computeHistogramPredivider(windowSize,
+					   static_cast<rkisp1_cif_isp_histogram_mode>(params->meas.hst_config.mode));
 
 	/* Update the configuration for histogram. */
 	params->module_cfg_update |= RKISP1_CIF_ISP_MODULE_HST;
diff --git a/src/ipa/rkisp1/algorithms/agc.h b/src/ipa/rkisp1/algorithms/agc.h
index 04b3247e1276..996fea71755c 100644
--- a/src/ipa/rkisp1/algorithms/agc.h
+++ b/src/ipa/rkisp1/algorithms/agc.h
@@ -44,11 +44,17 @@ public:
 		     ControlList &metadata) override;
 
 private:
+	int parseMeteringModes(IPAContext &context, const YamlObject &tuningData);
+	uint8_t computeHistogramPredivider(Size &size,
+					   enum rkisp1_cif_isp_histogram_mode mode);
+
 	void fillMetadata(IPAContext &context, IPAFrameContext &frameContext,
 			  ControlList &metadata);
 	double estimateLuminance(double gain) const override;
 
 	Span<const uint8_t> expMeans_;
+
+	std::map<int32_t, std::vector<uint8_t>> meteringModes_;
 };
 
 } /* namespace ipa::rkisp1::algorithms */
-- 
2.39.2