[libcamera-devel] [PATCH v2 1/4] ipa: raspberrypi: Allow long exposure modes for imx477.

[Naushir Patuck]

Update the imx477 CamHelper to use long exposure modes if needed.
This is done by overloading the CamHelper::GetVBlanking function to return a
frame length (and vblank value) computed using a scaling factor when the value
would be larger than what the sensor register could otherwise hold.

CamHelperImx477::Prepare is also overloaded to ensure that the "device.status"
metadata returns the right value if the long exposure scaling factor is used.
The scaling factor is unfortunately not returned back in metadata.

With the current imx477 driver, we can achieve a maximum exposure time of approx
127 seconds since the HBLANK control is read-only.

Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
---
 src/ipa/raspberrypi/cam_helper_imx477.cpp | 69 +++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/src/ipa/raspberrypi/cam_helper_imx477.cpp b/src/ipa/raspberrypi/cam_helper_imx477.cpp
index 4098fde6f322..139cc7dbd39a 100644
--- a/src/ipa/raspberrypi/cam_helper_imx477.cpp
+++ b/src/ipa/raspberrypi/cam_helper_imx477.cpp
@@ -6,6 +6,7 @@
  */
 
 #include <assert.h>
+#include <cmath>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -14,6 +15,7 @@
 #include "md_parser.hpp"
 
 using namespace RPiController;
+using libcamera::utils::Duration;
 
 /*
  * We care about two gain registers and a pair of exposure registers. Their
@@ -31,6 +33,9 @@ public:
 	CamHelperImx477();
 	uint32_t GainCode(double gain) const override;
 	double Gain(uint32_t gain_code) const override;
+	void Prepare(libcamera::Span<const uint8_t> buffer, Metadata &metadata) override;
+	uint32_t GetVBlanking(Duration &exposure, Duration minFrameDuration,
+			      Duration maxFrameDuration) const override;
 	void GetDelays(int &exposure_delay, int &gain_delay,
 		       int &vblank_delay) const override;
 	bool SensorEmbeddedDataPresent() const override;
@@ -41,6 +46,10 @@ private:
 	 * in units of lines.
 	 */
 	static constexpr int frameIntegrationDiff = 22;
+	/* Maximum frame length allowable for long exposure calculations. */
+	static constexpr int frameLengthMax = 0xffdc;
+	/* Largest long exposure scale factor given as a left shift on the frame length. */
+	static constexpr int longExposureShiftMax = 7;
 
 	void PopulateMetadata(const MdParser::RegisterMap &registers,
 			      Metadata &metadata) const override;
@@ -61,6 +70,66 @@ double CamHelperImx477::Gain(uint32_t gain_code) const
 	return 1024.0 / (1024 - gain_code);
 }
 
+void CamHelperImx477::Prepare(libcamera::Span<const uint8_t> buffer, Metadata &metadata)
+{
+	DeviceStatus deviceStatus, parsedStatus;
+
+	/* Get the device status provided by DelayedControls */
+	if (metadata.Get("device.status", deviceStatus) != 0)
+		return;
+
+	/* Get the device status provided by the embedded data buffer. */
+	CamHelper::parseEmbeddedData(buffer, metadata);
+	metadata.Get("device.status", parsedStatus);
+
+	/*
+	 * If the ratio of DelayedControls to embedded data shutter speed is > 1
+	 * and is a factor of 2^N, then we can assume this is a long exposure mode
+	 * frame. Since embedded data does not provide any hints of long exposure
+	 * modes, make sure we use the DelayedControls values in the metadata.
+	 * Otherwise, just go with the embedded data values.
+	 */
+	unsigned long ratio = std::lround(deviceStatus.shutter_speed / parsedStatus.shutter_speed);
+	bool replace = (ratio > 1) && ((ratio & (~ratio + 1)) == ratio);
+
+	if (replace)
+		metadata.Set("device.status", deviceStatus);
+}
+
+uint32_t CamHelperImx477::GetVBlanking(Duration &exposure,
+				       Duration minFrameDuration,
+				       Duration maxFrameDuration) const
+{
+	uint32_t frameLength, exposureLines;
+	unsigned int shift = 0;
+
+	frameLength = mode_.height + CamHelper::GetVBlanking(exposure, minFrameDuration,
+							     maxFrameDuration);
+	/*
+	 * Check if the frame length calculated needs to be setup for long
+	 * exposure mode. This will require us to use a long exposure scale
+	 * factor provided by a shift operation in the sensor.
+	 */
+	while (frameLength > frameLengthMax) {
+		if (++shift > longExposureShiftMax) {
+			shift = longExposureShiftMax;
+			frameLength = frameLengthMax;
+			break;
+		}
+		frameLength >>= 1;
+	}
+
+	if (shift) {
+		/* Account for any rounding in the scaled frame length value. */
+		frameLength <<= shift;
+		exposureLines = CamHelper::ExposureLines(exposure);
+		exposureLines = std::min(exposureLines, frameLength - frameIntegrationDiff);
+		exposure = CamHelper::Exposure(exposureLines);
+	}
+
+	return frameLength - mode_.height;
+}
+
 void CamHelperImx477::GetDelays(int &exposure_delay, int &gain_delay,
 				int &vblank_delay) const
 {
-- 
2.25.1