[libcamera-devel] [PATCH v2 2/6] libcamera: uvcvideo: Update exposure/gain ctrls set with new units

[Naushir Patuck]

The ManualExposure 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 ManualGain 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.cpp | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/libcamera/pipeline/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo.cpp
index 29afb121..aff86803 100644
--- a/src/libcamera/pipeline/uvcvideo.cpp
+++ b/src/libcamera/pipeline/uvcvideo.cpp
@@ -245,9 +245,22 @@ int PipelineHandlerUVC::processControls(UVCCameraData *data, Request *request)
 			controls.set(V4L2_CID_SATURATION, value);
 		} else if (id == controls::ManualExposure) {
 			controls.set(V4L2_CID_EXPOSURE_AUTO, static_cast<int32_t>(1));
-			controls.set(V4L2_CID_EXPOSURE_ABSOLUTE, value);
+			/*
+			 * controls::ManualExposure is in units of 1 us, and UVC
+			 * expects V4L2_CID_EXPOSURE_ABSOLUTE in units of 100 us.
+			 * So divide by 100 when setting the control.
+			 */
+			controls.set(V4L2_CID_EXPOSURE_ABSOLUTE, value.get<int32_t>() / 100);
 		} else if (id == controls::ManualGain) {
-			controls.set(V4L2_CID_GAIN, value);
+			/*
+			 * controls::ManualGain is specified as an absolute float value.
+			 * Map this in a linear way such that 1.0 -> default gain
+			 * of the V4L2_CID_GAIN control.
+			 */
+			ControlRange gainInfo = controls.infoMap()->at(V4L2_CID_GAIN);
+			float requestGain = value.get<float>();
+			int32_t gain = requestGain * gainInfo.def().get<int32_t>();
+			controls.set(V4L2_CID_GAIN, gain);
 		}
 	}
 
-- 
2.17.1