ipa: rkisp1: Add basic compression algorithm

The i.MX8 M Plus has a compression curve inside the compand block.  This
curve is necessary to process HDR stitched data and is useful for other
aspects like applying a digital gain to the incoming sensor data.

Add a basic algorithm for the compression curve. This algorithm has a
hardcoded input width of 20bit and output width of 12bit which matches
the imx8mp pipeline. Only a static gain is supported in this version.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/rkisp1/algorithms/compress.cpp

@@ -0,0 +1,103 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2025, Ideas On Board
+ *
+ * RkISP1 Compression curve
+ */
+#include "compress.h"
+
+#include <linux/videodev2.h>
+
+#include <libcamera/base/log.h>
+#include <libcamera/base/utils.h>
+
+#include "linux/rkisp1-config.h"
+
+/**
+ * \file compress.h
+ */
+
+namespace libcamera {
+
+namespace ipa::rkisp1::algorithms {
+
+/**
+ * \class Compress
+ * \brief RkISP1 Compress curve
+ *
+ * This algorithm implements support for the compression curve in the compand
+ * block available in the i.MX8 M Plus
+ *
+ * In its current version it only supports a static gain. This is useful for
+ * the agc algorithm to compensate for exposure/gain quantization effects.
+ *
+ * This algorithm doesn't have any configuration options. It needs to be
+ * configured per frame by other algorithms.
+ *
+ * Other algorithms can check configuration.compress.supported to see if
+ * compression is available. If it is available they can configure it per frame
+ * using frameContext.compress.enable and frameContext.compress.gain.
+ */
+
+LOG_DEFINE_CATEGORY(RkISP1Compress)
+
+constexpr static int kRkISP1CompressInBits = 20;
+constexpr static int kRkISP1CompressOutBits = 12;
+
+/**
+ * \copydoc libcamera::ipa::Algorithm::configure
+ */
+int Compress::configure(IPAContext &context,
+			[[maybe_unused]] const IPACameraSensorInfo &configInfo)
+{
+	if (context.configuration.paramFormat != V4L2_META_FMT_RK_ISP1_EXT_PARAMS ||
+	    !context.hw->compand) {
+		LOG(RkISP1Compress, Warning)
+			<< "Compression is not supported by the hardware or kernel.";
+		return 0;
+	}
+
+	context.configuration.compress.supported = true;
+	return 0;
+}
+
+/**
+ * \copydoc libcamera::ipa::Algorithm::prepare
+ */
+void Compress::prepare([[maybe_unused]] IPAContext &context,
+		       [[maybe_unused]] const uint32_t frame,
+		       IPAFrameContext &frameContext,
+		       RkISP1Params *params)
+{
+	if (!context.configuration.compress.supported)
+		return;
+
+	auto comp = params->block<BlockType::CompandCompress>();
+	comp.setEnabled(frameContext.compress.enable);
+
+	if (!frameContext.compress.enable)
+		return;
+
+	int xmax = (1 << kRkISP1CompressInBits);
+	int ymax = (1 << kRkISP1CompressOutBits);
+	int inLogStep = std::log2(xmax / RKISP1_CIF_ISP_COMPAND_NUM_POINTS);
+
+	for (unsigned int i = 0; i < RKISP1_CIF_ISP_COMPAND_NUM_POINTS; i++) {
+		double x = (i + 1) * (1.0 / RKISP1_CIF_ISP_COMPAND_NUM_POINTS);
+		double y = x * frameContext.compress.gain;
+
+		comp->px[i] = inLogStep;
+		comp->x[i] = std::min<int>(x * xmax, xmax - 1);
+		comp->y[i] = std::min<int>(y * ymax, ymax - 1);
+	}
+
+	LOG(RkISP1Compress, Debug) << "Compression: " << kRkISP1CompressInBits
+				   << " bits to " << kRkISP1CompressOutBits
+				   << " bits gain: " << frameContext.compress.gain;
+}
+
+REGISTER_IPA_ALGORITHM(Compress, "Compress")
+
+} /* namespace ipa::rkisp1::algorithms */
+
+} /* namespace libcamera */

src/ipa/rkisp1/algorithms/compress.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2025, Ideas On Board
+ *
+ * RkISP1 Compression curve
+ */
+
+#pragma once
+
+#include "algorithm.h"
+
+namespace libcamera {
+
+namespace ipa::rkisp1::algorithms {
+
+class Compress : public Algorithm
+{
+public:
+	Compress() = default;
+	~Compress() = default;
+
+	int configure(IPAContext &context,
+		      const IPACameraSensorInfo &configInfo) override;
+	void prepare(IPAContext &context, const uint32_t frame,
+		     IPAFrameContext &frameContext,
+		     RkISP1Params *params) override;
+};
+
+} /* namespace ipa::rkisp1::algorithms */
+} /* namespace libcamera */

src/ipa/rkisp1/algorithms/meson.build

@@ -5,6 +5,7 @@ rkisp1_ipa_algorithms = files([
     'awb.cpp',
     'blc.cpp',
     'ccm.cpp',
+    'compress.cpp',
     'cproc.cpp',
     'dpcc.cpp',
     'dpf.cpp',

src/ipa/rkisp1/ipa_context.cpp

@@ -66,6 +66,14 @@ namespace libcamera::ipa::rkisp1 {
  * operates in manual or automatic mode.
  */
 
+/**
+ * \var IPASessionConfiguration::compress
+ * \brief Compress parameters configuration of the IPA
+ *
+ * \var IPASessionConfiguration::agc.supported
+ * \brief true if compression is supported and the algorithm is loaded
+ */
+
 /**
  * \var IPASessionConfiguration::lsc
  * \brief Lens Shading Correction configuration of the IPA
@@ -377,6 +385,17 @@ namespace libcamera::ipa::rkisp1 {
  * \brief Colour Correction Matrix
  */
 
+/**
+ * \var IPAFrameContext::compress
+ * \brief Compress parameters for this frame
+ *
+ * \struct IPAFrameContext::compress.enable
+ * \brief True if compression is enabled
+ *
+ * \var IPAFrameContext::compress.gain
+ * \brief The gain applied with the compression curve
+ */
+
 /**
  * \var IPAFrameContext::cproc
  * \brief Color Processing parameters for this frame

src/ipa/rkisp1/ipa_context.h

@@ -49,6 +49,10 @@ struct IPASessionConfiguration {
 		bool enabled;
 	} awb;
 
+	struct {
+		bool supported;
+	} compress;
+
 	struct {
 		bool enabled;
 	} lsc;
@@ -158,6 +162,11 @@ struct IPAFrameContext : public FrameContext {
 		bool update;
 	} cproc;
 
+	struct {
+		bool enable;
+		double gain;
+	} compress;
+
 	struct {
 		bool denoise;
 		bool update;