libcamera: controls: Define a default lens position behaviour

Update the AfMode control description to explicitly define a
startup/default behaviour.

On startup, the camera will move the lens to the position given by the
default value of the LensPosition control if operating in manual focus
mode. Typically this would be the hyperfocal position of the lens.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/control_ids.yaml

@@ -408,6 +408,13 @@ controls:
             LensPosition control.
 
             In this mode the AfState will always report AfStateIdle.
+
+            If the camera is started in AfModeManual, it will move the focus
+            lens to the position specified by the LensPosition control.
+
+            This mode is the recommended default value for the AfMode control.
+            External cameras (as reported by the Location property set to
+            CameraLocationExternal) may use a different default value.
         - name: AfModeAuto
           value: 1
           description: |