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libcamera: Document sensor driver requirements

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Document the feature an image sensor driver has to provide to be
fully libcamera-compliant.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
This commit is contained in:
Jacopo Mondi 2020-12-30 18:02:48 +01:00
parent 7415c139cd
commit 1b4997ef08
3 changed files with 66 additions and 0 deletions
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Documentation/index.rst
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@ -18,3 +18,4 @@
Pipeline Handler Writer's Guide <guides/pipeline-handler>
Tracing guide <guides/tracing>
Environment variables <environment_variables>
Sensor driver requirements <sensor_driver_requirements>

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Documentation/meson.build
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@ -57,6 +57,7 @@ if sphinx.found()
'guides/pipeline-handler.rst',
'guides/tracing.rst',
'index.rst',
'sensor_driver_requirements.rst',
'../README.rst',
]

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Documentation/sensor_driver_requirements.rst Normal file
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.. SPDX-License-Identifier: CC-BY-SA-4.0
.. _sensor-driver-requirements:
Sensor Driver Requirements
==========================
libcamera handles imaging devices in the CameraSensor class and defines
through its API a consistent interface towards other library components.
The CameraSensor class uses the V4L2 subdev kernel API to interface with the
camera sensor through one or multiple sub-devices exposed in userspace by
the sensor driver.
In order for libcamera to be fully operational and provide to applications and
pipeline handlers all the required information to interface with the camera
sensor, a set of mandatory and optional features the driver has to support
has been defined.
Mandatory Requirements
----------------------
The sensor driver is assumed to be fully compliant with the V4L2 specification.
The sensor driver shall support the following V4L2 controls:
* `V4L2_CID_HBLANK`_
* `V4L2_CID_PIXEL_RATE`_
.. _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
Both controls are used to compute the sensor output timings.
Optional Requirements
---------------------
The sensor driver should support the following V4L2 controls:
* `V4L2_CID_CAMERA_ORIENTATION`_
* `V4L2_CID_CAMERA_SENSOR_ROTATION`_
.. _V4L2_CID_CAMERA_ORIENTATION: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-camera.html
.. _V4L2_CID_CAMERA_SENSOR_ROTATION: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-process.html
The controls are used to register the camera location and orientation.
The sensor driver should implement support for the V4L2 Selection API,
specifically it should implement support for the
`VIDIOC_SUBDEV_G_SELECTION`_ ioctl with support for the following selection
targets:
.. _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
* `V4L2_SEL_TGT_CROP_BOUNDS`_ to report the readable pixel array area size
* `V4L2_SEL_TGT_CROP_DEFAULT`_ to report the active pixel array area size
* `V4L2_SEL_TGT_CROP`_ to report the analogue selection rectangle
Support for the selection API is scheduled to become a mandatory feature in
the near future.
.. _V4L2_SEL_TGT_CROP_BOUNDS: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/v4l2-selection-targets.html
.. _V4L2_SEL_TGT_CROP_DEFAULT: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/v4l2-selection-targets.html
.. _V4L2_SEL_TGT_CROP: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/v4l2-selection-targets.html