Documentation: v4l: Document rotation and orientation for sensor drivers

Document how rotation and orientation should be taken into account in
writing camera sensor drivers.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Documentation/driver-api/media/camera-sensor.rst

@@ -151,3 +151,25 @@ used to obtain device's power state after the power state transition:
 The function returns a non-zero value if it succeeded getting the power count or
 runtime PM was disabled, in either of which cases the driver may proceed to
 access the device.
+
+Rotation, orientation and flipping
+----------------------------------
+
+Some systems have the camera sensor mounted upside down compared to its natural
+mounting rotation. In such cases, drivers shall expose the information to
+userspace with the :ref:`V4L2_CID_CAMERA_SENSOR_ROTATION
+<v4l2-camera-sensor-rotation>` control.
+
+Sensor drivers shall also report the sensor's mounting orientation with the
+:ref:`V4L2_CID_CAMERA_SENSOR_ORIENTATION <v4l2-camera-sensor-orientation>`.
+
+Use ``v4l2_fwnode_device_parse()`` to obtain rotation and orientation
+information from system firmware and ``v4l2_ctrl_new_fwnode_properties()`` to
+register the appropriate controls.
+
+Sensor drivers that have any vertical or horizontal flips embedded in the
+register programming sequences shall initialize the V4L2_CID_HFLIP and
+V4L2_CID_VFLIP controls with the values programmed by the register sequences.
+The default values of these controls shall be 0 (disabled). Especially these
+controls shall not be inverted, independently of the sensor's mounting
+rotation.

Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst

@@ -506,6 +506,8 @@ enum v4l2_scene_mode -
     value down. A value of zero stops the motion if one is in progress
     and has no effect otherwise.
 
+.. _v4l2-camera-sensor-orientation:
+
 ``V4L2_CID_CAMERA_ORIENTATION (menu)``
     This read-only control describes the camera orientation by reporting its
     mounting position on the device where the camera is installed. The control
@@ -536,6 +538,7 @@ enum v4l2_scene_mode -
       - The camera is not directly attached to the device and is freely movable.
 
 
+.. _v4l2-camera-sensor-rotation:
 
 ``V4L2_CID_CAMERA_SENSOR_ROTATION (integer)``
     This read-only control describes the rotation correction in degrees in the