ipa: raspberrypi: Add camera helper for Sony IMX296 sensor

The Sony IMX296 sensor has an exponential gain model, and adds a fixed
14.26µs offset to the exposure time expressed in line units.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/raspberrypi/cam_helper_imx296.cpp

@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2020, Raspberry Pi (Trading) Limited
+ *
+ * cam_helper_imx296.cpp - Camera helper for IMX296 sensor
+ */
+
+#include <algorithm>
+#include <cmath>
+#include <stddef.h>
+
+#include "cam_helper.hpp"
+
+using namespace RPiController;
+using libcamera::utils::Duration;
+using namespace std::literals::chrono_literals;
+
+class CamHelperImx296 : public CamHelper
+{
+public:
+	CamHelperImx296();
+	uint32_t GainCode(double gain) const override;
+	double Gain(uint32_t gain_code) const override;
+	uint32_t ExposureLines(Duration exposure) const override;
+	Duration Exposure(uint32_t exposure_lines) const override;
+
+private:
+	static constexpr uint32_t maxGainCode = 239;
+	static constexpr Duration timePerLine = 550.0 / 37.125e6 * 1.0s;
+
+	/*
+	 * Smallest difference between the frame length and integration time,
+	 * in units of lines.
+	 */
+	static constexpr int frameIntegrationDiff = 4;
+};
+
+CamHelperImx296::CamHelperImx296()
+	: CamHelper(nullptr, frameIntegrationDiff)
+{
+}
+
+uint32_t CamHelperImx296::GainCode(double gain) const
+{
+	uint32_t code = 20 * std::log10(gain) * 10;
+	return std::min(code, maxGainCode);
+}
+
+double CamHelperImx296::Gain(uint32_t gain_code) const
+{
+	return std::pow(10.0, gain_code / 200.0);
+}
+
+uint32_t CamHelperImx296::ExposureLines(Duration exposure) const
+{
+	return (exposure - 14.26us) / timePerLine;
+}
+
+Duration CamHelperImx296::Exposure(uint32_t exposure_lines) const
+{
+	return exposure_lines * timePerLine + 14.26us;
+}
+
+static CamHelper *Create()
+{
+	return new CamHelperImx296();
+}
+
+static RegisterCamHelper reg("imx296", &Create);

src/ipa/raspberrypi/meson.build

@@ -21,6 +21,7 @@ rpi_ipa_sources = files([
     'cam_helper_ov5647.cpp',
     'cam_helper_imx219.cpp',
     'cam_helper_imx290.cpp',
+    'cam_helper_imx296.cpp',
     'cam_helper_imx477.cpp',
     'cam_helper_imx519.cpp',
     'cam_helper_ov9281.cpp',