[libcamera-devel] [PATCH v7 01/10] libcamera: Document sensor driver requirements

[Jacopo Mondi]

Hi Kieran,

On Mon, Jan 18, 2021 at 09:59:55AM +0000, Kieran Bingham wrote:
> Hi Jacopo,

The series has just been pushed.

I can work on-top

>
> On 15/01/2021 17:00, Jacopo Mondi wrote:
> > Document the feature an image sensor driver has to provide to be
> > fully libcamera-compliant.
> >
> > Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > Reviewed-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> > Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> > ---
> >  Documentation/index.rst                      |  1 +
> >  Documentation/meson.build                    |  1 +
> >  Documentation/sensor_driver_requirements.rst | 64 ++++++++++++++++++++
> >  3 files changed, 66 insertions(+)
> >  create mode 100644 Documentation/sensor_driver_requirements.rst
> >
> > diff --git a/Documentation/index.rst b/Documentation/index.rst
> > index c49db18d52bd..285ca7c3e5ae 100644
> > --- a/Documentation/index.rst
> > +++ b/Documentation/index.rst
> > @@ -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>
> > diff --git a/Documentation/meson.build b/Documentation/meson.build
> > index b1f5bb52474c..9950465ded6e 100644
> > --- a/Documentation/meson.build
> > +++ b/Documentation/meson.build
> > @@ -57,6 +57,7 @@ if sphinx.found()
> >          'guides/pipeline-handler.rst',
> >          'guides/tracing.rst',
> >          'index.rst',
> > +        'sensor_driver_requirements.rst',
> >         '../README.rst',
> >      ]
> >
> > diff --git a/Documentation/sensor_driver_requirements.rst b/Documentation/sensor_driver_requirements.rst
> > new file mode 100644
> > index 000000000000..0e658aaa03b5
> > --- /dev/null
> > +++ b/Documentation/sensor_driver_requirements.rst
> > @@ -0,0 +1,64 @@
> > +.. 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.
>
> Optional change:
>
> 'and defines a consistent interface through it's API towards other'
>
> > +
> > +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
>
> Another re-order:
>
> 'and provide all the required information to interface with the camera
> sensor to applications,'
>
>
> Both of those are perfectly understandable as you have written them,
> it's just that we wouldn't write it in that order in English ;-)
>
> No idea why or what the grammar rules are, that's just a pure 'I'd write
> that the other way' warning light fired in my head.
>
>
> So - no need to change if you don't want to.
>
> > +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.
>
> Should that read the camera location and rotation?
>
> Given the above and the definition of V4L2_CID_CAMERA_ORIENTATION, I
> think the orientation is the 'location'...
>
>
> With those updated or not as you see fit:
>
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
>
> > +
> > +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
> >
>
> --
> Regards
> --
> Kieran