1.. SPDX-License-Identifier: GPL-2.0 2 3.. _media_using_camera_sensor_drivers: 4 5Using camera sensor drivers 6=========================== 7 8This section describes common practices for how the V4L2 sub-device interface is 9used to control the camera sensor drivers. 10 11You may also find :ref:`media_writing_camera_sensor_drivers` useful. 12 13Frame size 14---------- 15 16There are two distinct ways to configure the frame size produced by camera 17sensors. 18 19Freely configurable camera sensor drivers 20~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 21 22Freely configurable camera sensor drivers expose the device's internal 23processing pipeline as one or more sub-devices with different cropping and 24scaling configurations. The output size of the device is the result of a series 25of cropping and scaling operations from the device's pixel array's size. 26 27An example of such a driver is the CCS driver. 28 29Register list based drivers 30~~~~~~~~~~~~~~~~~~~~~~~~~~~ 31 32Register list based drivers generally, instead of able to configure the device 33they control based on user requests, are limited to a number of preset 34configurations that combine a number of different parameters that on hardware 35level are independent. How a driver picks such configuration is based on the 36format set on a source pad at the end of the device's internal pipeline. 37 38Most sensor drivers are implemented this way. 39 40Frame interval configuration 41---------------------------- 42 43There are two different methods for obtaining possibilities for different frame 44intervals as well as configuring the frame interval. Which one to implement 45depends on the type of the device. 46 47Raw camera sensors 48~~~~~~~~~~~~~~~~~~ 49 50Instead of a high level parameter such as frame interval, the frame interval is 51a result of the configuration of a number of camera sensor implementation 52specific parameters. Luckily, these parameters tend to be the same for more or 53less all modern raw camera sensors. 54 55The frame interval is calculated using the following equation:: 56 57 frame interval = (analogue crop width + horizontal blanking) * 58 (analogue crop height + vertical blanking) / pixel rate 59 60The formula is bus independent and is applicable for raw timing parameters on 61large variety of devices beyond camera sensors. Devices that have no analogue 62crop, use the full source image size, i.e. pixel array size. 63 64Horizontal and vertical blanking are specified by ``V4L2_CID_HBLANK`` and 65``V4L2_CID_VBLANK``, respectively. The unit of the ``V4L2_CID_HBLANK`` control 66is pixels and the unit of the ``V4L2_CID_VBLANK`` is lines. The pixel rate in 67the sensor's **pixel array** is specified by ``V4L2_CID_PIXEL_RATE`` in the same 68sub-device. The unit of that control is pixels per second. 69 70Register list based drivers need to implement read-only sub-device nodes for the 71purpose. Devices that are not register list based need these to configure the 72device's internal processing pipeline. 73 74The first entity in the linear pipeline is the pixel array. The pixel array may 75be followed by other entities that are there to allow configuring binning, 76skipping, scaling or digital crop, see :ref:`VIDIOC_SUBDEV_G_SELECTION 77<VIDIOC_SUBDEV_G_SELECTION>`. 78 79USB cameras etc. devices 80~~~~~~~~~~~~~~~~~~~~~~~~ 81 82USB video class hardware, as well as many cameras offering a similar higher 83level interface natively, generally use the concept of frame interval (or frame 84rate) on device level in firmware or hardware. This means lower level controls 85implemented by raw cameras may not be used on uAPI (or even kAPI) to control the 86frame interval on these devices. 87 88Rotation, orientation and flipping 89---------------------------------- 90 91Some systems have the camera sensor mounted upside down compared to its natural 92mounting rotation. In such cases, drivers shall expose the information to 93userspace with the :ref:`V4L2_CID_CAMERA_SENSOR_ROTATION 94<v4l2-camera-sensor-rotation>` control. 95 96Sensor drivers shall also report the sensor's mounting orientation with the 97:ref:`V4L2_CID_CAMERA_SENSOR_ORIENTATION <v4l2-camera-sensor-orientation>`. 98 99Sensor drivers that have any vertical or horizontal flips embedded in the 100register programming sequences shall initialize the :ref:`V4L2_CID_HFLIP 101<v4l2-cid-hflip>` and :ref:`V4L2_CID_VFLIP <v4l2-cid-vflip>` controls with the 102values programmed by the register sequences. The default values of these 103controls shall be 0 (disabled). Especially these controls shall not be inverted, 104independently of the sensor's mounting rotation. 105