[libcamera-devel] [PATCH v3 2/5] libcamera: uvcvideo: Update exposure/gain ctrls set with new units

[Naushir Patuck]

The ExposureTime control now uses units of 1 micro-second, and UVC
uses units of 100 micro-seconds. Correctly map the values before
setting V4L2_CID_EXPOSURE_ABSOLUTE on the V4L2 device.

The AnalogueGain control now uses floats to allow fractional gain
values. Since UVC has no explicit gain units, map the default gain value
to 1.0 and linearly map to the requested value.

Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
---
 src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
index d7df95e4..9d589f69 100644
--- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
+++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
@@ -253,9 +253,22 @@ int PipelineHandlerUVC::processControls(UVCCameraData *data, Request *request)
 			controls.set(V4L2_CID_SATURATION, value);
 		} else if (id == controls::ExposureTime) {
 			controls.set(V4L2_CID_EXPOSURE_AUTO, static_cast<int32_t>(1));
-			controls.set(V4L2_CID_EXPOSURE_ABSOLUTE, value);
+			/*
+			 * controls::ExposureTime is in units of 1 us, and UVC
+			 * expects V4L2_CID_EXPOSURE_ABSOLUTE in units of 100 us.
+			 */
+			controls.set(V4L2_CID_EXPOSURE_ABSOLUTE,
+				     value.get<int32_t>() / 100);
 		} else if (id == controls::AnalogueGain) {
-			controls.set(V4L2_CID_GAIN, value);
+			/*
+			 * controls::AnalogueGain is specified as an absolute
+			 * multiplier for all RGB samples. Map this multiplier
+			 * in a linear way such that 1.0 -> default gain
+			 * of the V4L2_CID_GAIN control on the uvcvideo device.
+			 */
+			const ControlInfo &gainInfo = controls.infoMap()->at(V4L2_CID_GAIN);
+			int32_t gain = value.get<float>() * gainInfo.def().get<int32_t>();
+			controls.set(V4L2_CID_GAIN, gain);
 		}
 	}
 
-- 
2.17.1