controls: Split FrameDurations into FrameDuration and FrameDurationLimits

We need a separate control to report the nominal frame duration, but
it's also useful to report the min/max frame duration values that will
be used. Split the FrameDurations control into FrameDuration and
FrameDurationLimits respectively to support both of these.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/control_ids.yaml

@@ -323,7 +323,14 @@ controls:
         step to respect the received gain factor and shall report
         their total value in the request metadata.
 
-  - FrameDurations:
+  - FrameDuration:
+      type: int64_t
+      description: |
+        The instantaneous frame duration from start of frame exposure to start
+        of next exposure, expressed in microseconds. This control is meant to
+        be returned in metadata.
+
+  - FrameDurationLimits:
       type: int64_t
       description: |
         The minimum and maximum (in that order) frame duration,

src/libcamera/pipeline/ipu3/ipu3.cpp

@@ -983,9 +983,10 @@ int PipelineHandlerIPU3::initControls(IPU3CameraData *data)
 		frameDurations[i] = frameSize / (sensorInfo.pixelRate / 1000000U);
 	}
 
-	controls[&controls::FrameDurations] = ControlInfo(frameDurations[0],
-							  frameDurations[1],
-							  frameDurations[2]);
+	controls[&controls::FrameDurationLimits] =
+		ControlInfo(frameDurations[0],
+			    frameDurations[1],
+			    frameDurations[2]);
 
 	/*
 	 * Compute the scaler crop limits.