libcamera: camera_sensor: Make VBLANK mandatory

Add the V4L2_CID_VBLANK control to the list of mandatory controls
the sensor driver has to report and document the new requirement.

The vertical blanking control is used to calculate the frame duration.

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

Documentation/sensor_driver_requirements.rst

@@ -27,18 +27,20 @@ The sensor driver shall support the following V4L2 controls:
 * `V4L2_CID_EXPOSURE`_
 * `V4L2_CID_HBLANK`_
 * `V4L2_CID_PIXEL_RATE`_
+* `V4L2_CID_VBLANK`_
 
 .. _V4L2_CID_EXPOSURE: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/control.html
 .. _V4L2_CID_HBLANK: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-source.html
 .. _V4L2_CID_PIXEL_RATE: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-process.html
+.. _V4L2_CID_VBLANK: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-source.html
 
 While V4L2 doesn't specify a unit for the `EXPOSURE` control, libcamera requires
 it to be expressed as a number of image lines. Camera sensor drivers that do not
 comply with this requirement will need to be adapted or will produce incorrect
 results.
 
-The `HBLANK` and `PIXEL_RATE` controls are used to compute the sensor output
-timings.
+The `HBLANK`, `PIXEL_RATE` and `VBLANK` controls are used to compute the sensor
+output timings.
 
 Optional Requirements
 ---------------------

src/libcamera/camera_sensor.cpp

@@ -244,6 +244,7 @@ int CameraSensor::validateSensorDriver()
 		V4L2_CID_EXPOSURE,
 		V4L2_CID_HBLANK,
 		V4L2_CID_PIXEL_RATE,
+		V4L2_CID_VBLANK,
 	};
 
 	ControlList ctrls = subdev_->getControls(mandatoryControls);