[libcamera-devel] [PATCH 1/2] ipa: camera_sensor_helper: Add AR0521 support

[Jacopo Mondi]

Add support for OnSemi AR0521 5Mpx image sensor to libipa.

The sensor implments a gain model realized via a piecewise exponential
gain function defined by a table available in the sensor's application
developer guide.

Add support for the sensor using a dedicated CameraSensorHelper
instance.

Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
---
 src/ipa/libipa/camera_sensor_helper.cpp | 45 +++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
index 35056bec80c3..cb5cdf1d1e54 100644
--- a/src/ipa/libipa/camera_sensor_helper.cpp
+++ b/src/ipa/libipa/camera_sensor_helper.cpp
@@ -366,6 +366,51 @@ static constexpr double expGainDb(double step)
 	return log2_10 * step / 20;
 }

+class CameraSensorHelperAr0521 : public CameraSensorHelper
+{
+public:
+	uint32_t gainCode(double gain) const override;
+	double gain(uint32_t gainCode) const override;
+
+private:
+	const unsigned int kStep_ = 16;
+};
+
+uint32_t CameraSensorHelperAr0521::gainCode(double gain) const
+{
+	unsigned int coarse = 0;
+
+	if (gain < 2.02) {
+		coarse = 0;
+	} else if (gain < 4.21) {
+		coarse = 1;
+	} else if (gain < 7.95) {
+		coarse = 2;
+	} else if (gain < 15.28) {
+		coarse = 3;
+	} else {
+		LOG(CameraSensorHelper, Error) << "Gain too high: " << gain;
+		gain = 15.28;
+		coarse = 3;
+	}
+
+	unsigned int exp = 1 << coarse;
+	unsigned int fine = kStep_ * (gain - exp) / exp;
+
+	return (coarse << 4) | (fine & 0xf);
+}
+
+double CameraSensorHelperAr0521::gain(uint32_t gainCode) const
+{
+	unsigned int coarse = gainCode >> 4;
+	unsigned int fine = gainCode & 0xf;
+	unsigned int exp = 1 << coarse;
+
+	return exp + (exp * fine / kStep_);
+}
+
+REGISTER_CAMERA_SENSOR_HELPER("ar0521", CameraSensorHelperAr0521)
+
 class CameraSensorHelperImx219 : public CameraSensorHelper
 {
 public:
--
2.38.1