021752924b
Add the V4L2_CID_EXPOSURE control to the list of mandatory controls the sensor driver has to report and document this new requirement. While at it, re-sort the mandatory V4L2 controls in alphabetical order in the CameraSensor class and remove the above comment as the usage of the controls is better reported in the documentation. Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
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3.1 KiB
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72 lines
3.1 KiB
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.. SPDX-License-Identifier: CC-BY-SA-4.0
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.. _sensor-driver-requirements:
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Sensor Driver Requirements
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==========================
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libcamera handles imaging devices in the CameraSensor class and defines
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a consistent interface through its API towards other library components.
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The CameraSensor class uses the V4L2 subdev kernel API to interface with the
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camera sensor through one or multiple sub-devices exposed in userspace by
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the sensor driver.
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In order for libcamera to be fully operational and provide all the required
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information to interface with the camera sensor to applications and pipeline
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handlers, a set of mandatory and optional features the driver has to support
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has been defined.
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Mandatory Requirements
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----------------------
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The sensor driver is assumed to be fully compliant with the V4L2 specification.
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The sensor driver shall support the following V4L2 controls:
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* `V4L2_CID_EXPOSURE`_
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* `V4L2_CID_HBLANK`_
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* `V4L2_CID_PIXEL_RATE`_
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.. _V4L2_CID_EXPOSURE: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/control.html
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.. _V4L2_CID_HBLANK: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-source.html
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.. _V4L2_CID_PIXEL_RATE: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-process.html
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While V4L2 doesn't specify a unit for the `EXPOSURE` control, libcamera requires
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it to be expressed as a number of image lines. Camera sensor drivers that do not
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comply with this requirement will need to be adapted or will produce incorrect
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results.
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The `HBLANK` and `PIXEL_RATE` controls are used to compute the sensor output
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timings.
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Optional Requirements
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---------------------
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The sensor driver should support the following V4L2 controls:
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* `V4L2_CID_CAMERA_ORIENTATION`_
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* `V4L2_CID_CAMERA_SENSOR_ROTATION`_
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.. _V4L2_CID_CAMERA_ORIENTATION: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-camera.html
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.. _V4L2_CID_CAMERA_SENSOR_ROTATION: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-process.html
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The controls are used to register the camera location and rotation.
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The sensor driver should implement support for the V4L2 Selection API,
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specifically it should implement support for the
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`VIDIOC_SUBDEV_G_SELECTION`_ ioctl with support for the following selection
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targets:
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.. _VIDIOC_SUBDEV_G_SELECTION: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/vidioc-subdev-g-selection.html?highlight=g_selection#c.V4L.VIDIOC_SUBDEV_G_SELECTION
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* `V4L2_SEL_TGT_CROP_BOUNDS`_ to report the readable pixel array area size
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* `V4L2_SEL_TGT_CROP_DEFAULT`_ to report the active pixel array area size
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* `V4L2_SEL_TGT_CROP`_ to report the analogue selection rectangle
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Support for the selection API is scheduled to become a mandatory feature in
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the near future.
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.. _V4L2_SEL_TGT_CROP_BOUNDS: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/v4l2-selection-targets.html
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.. _V4L2_SEL_TGT_CROP_DEFAULT: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/v4l2-selection-targets.html
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.. _V4L2_SEL_TGT_CROP: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/v4l2-selection-targets.html
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