[PATCH v2 1/2] test: ipa: libipa: Add CameraSensorHelper Gain Model tests

[Kieran Bingham]

Introduce a test that validates conversion of the gain model
in both Linear and Exponential models.

It should be expected that if a gainCode produces a given gain
value, then converting that gain back should produce the same
result.

The test is known to fail and is marked as such. The test will be
updated with the corresponding fix.

Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
---
 test/ipa/camera_sensor_helper.cpp | 101 ++++++++++++++++++++++++++++++
 test/ipa/meson.build              |   5 +-
 2 files changed, 105 insertions(+), 1 deletion(-)
 create mode 100644 test/ipa/camera_sensor_helper.cpp

diff --git a/test/ipa/camera_sensor_helper.cpp b/test/ipa/camera_sensor_helper.cpp
new file mode 100644
index 000000000000..d8a8c6850a04
--- /dev/null
+++ b/test/ipa/camera_sensor_helper.cpp
@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2024, Ideas on Board Oy.
+ */
+
+#include "libipa/camera_sensor_helper.h"
+
+#include <iostream>
+#include <string.h>
+
+#include "test.h"
+
+using namespace std;
+using namespace libcamera;
+using namespace libcamera::ipa;
+
+/*
+ * Helper function to compute the m parameter of the exponential gain model
+ * when the gain code is expressed in dB.
+ */
+static constexpr double expGainDb(double step)
+{
+	constexpr double log2_10 = 3.321928094887362;
+
+	/*
+         * The gain code is expressed in step * dB (e.g. in 0.1 dB steps):
+         *
+         * G_code = G_dB/step = 20/step*log10(G_linear)
+         *
+         * Inverting the formula, we get
+         *
+         * G_linear = 10^(step/20*G_code) = 2^(log2(10)*step/20*G_code)
+         */
+	return log2_10 * step / 20;
+}
+
+class CameraSensorHelperExponential : public CameraSensorHelper
+{
+public:
+	CameraSensorHelperExponential()
+	{
+		gainType_ = AnalogueGainExponential;
+		gainConstants_.exp = { 1.0, expGainDb(0.3) };
+	}
+};
+
+class CameraSensorHelperLinear : public CameraSensorHelper
+{
+public:
+	CameraSensorHelperLinear()
+	{
+		gainType_ = AnalogueGainLinear;
+		gainConstants_.linear = { 0, 1024, -1, 1024 };
+	}
+};
+
+class CameraSensorHelperTest : public Test
+{
+protected:
+	int testGainModel(CameraSensorHelper &helper)
+	{
+		int ret = TestPass;
+
+		/*
+		 * Arbitrarily test 255 code positions assuming 8 bit fields
+		 * are the normal maximum for a gain code register.
+		 */
+		for (unsigned int i = 0; i < 255; i++) {
+			float gain = helper.gain(i);
+			uint32_t gainCode = helper.gainCode(gain);
+
+			if (i != gainCode) {
+				std::cout << "Gain conversions failed: "
+					  << i << " : " << gain << " : "
+					  << gainCode << std::endl;
+
+				ret = TestFail;
+			}
+		};
+
+		return ret;
+	}
+
+	int run() override
+	{
+		unsigned int failures = 0;
+
+		CameraSensorHelperExponential exponential;
+		CameraSensorHelperLinear linear;
+
+		if (testGainModel(exponential) == TestFail)
+			failures++;
+
+		if (testGainModel(linear) == TestFail)
+			failures++;
+
+		return failures ? TestFail : TestPass;
+	}
+};
+
+TEST_REGISTER(CameraSensorHelperTest)
diff --git a/test/ipa/meson.build b/test/ipa/meson.build
index 180b0da0a51a..abc2456fc341 100644
--- a/test/ipa/meson.build
+++ b/test/ipa/meson.build
@@ -1,6 +1,8 @@
 # SPDX-License-Identifier: CC0-1.0
 
 ipa_test = [
+    {'name': 'camera_sensor_helper', 'sources': ['camera_sensor_helper.cpp'],
+     'should_fail': true},
     {'name': 'ipa_module_test', 'sources': ['ipa_module_test.cpp']},
     {'name': 'ipa_interface_test', 'sources': ['ipa_interface_test.cpp']},
 ]
@@ -11,5 +13,6 @@ foreach test : ipa_test
                      link_with : [libipa, test_libraries],
                      include_directories : [libipa_includes, test_includes_internal])
 
-    test(test['name'], exe, suite : 'ipa')
+    test(test['name'], exe, suite : 'ipa',
+         should_fail : test.get('should_fail', false))
 endforeach
-- 
2.34.1