[libcamera-devel] [PATCH 02/12] libcamera: camera_sensor: Make V4L2_CID_EXPOSURE mandatory

[Laurent Pinchart]

Hi Jacopo,

Thank you for the patch.

On Tue, Jan 05, 2021 at 08:05:12PM +0100, Jacopo Mondi wrote:
> Add the V4L2_CID_EXPOSURE control to the list of mandatory controls the
> sensor driver has to report and document this new requirement.
> 
> Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> ---
>  Documentation/sensor_driver_requirements.rst | 11 ++++++++++-
>  src/libcamera/camera_sensor.cpp              |  1 +
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/sensor_driver_requirements.rst b/Documentation/sensor_driver_requirements.rst
> index 0e658aaa03b5..97e98b9e12ef 100644
> --- a/Documentation/sensor_driver_requirements.rst
> +++ b/Documentation/sensor_driver_requirements.rst
> @@ -26,11 +26,20 @@ The sensor driver shall support the following V4L2 controls:
>  
>  * `V4L2_CID_HBLANK`_
>  * `V4L2_CID_PIXEL_RATE`_
> +* `V4L2_CID_EXPOSURE`_
>  
>  .. _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
> +.. _V4L2_CID_EXPOSURE: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/control.html

Could you keep these alphabetically sorted, here, below and in the code
?

> +
> +The `HBLANK` and `PIXEL_RATE` controls are used to compute the sensor
> +output timings.
> +
> +The `EXPOSURE` control shall report the image integration time in number of
> +lines. The V4L2 documentation does not specify a unit for this control, drivers
> +compliant with the V4L2 specification might need to be changed to be used by
> +libcamera.

I'm not sure why I would have gone for the opposite order (V4L2 first,
then libcamera) so you can ignore the following if you wish.

While V4L2 doesn't specify a unit for the `EXPOSURE` control, libcamera requires
it to be expressed as a number of image lines. Camera sensor drivers that do not
comply with this requirement will need to be adapted or will produce incorrect
results.

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

>  
> -Both controls are used to compute the sensor output timings.
>  
>  Optional Requirements
>  ---------------------
> diff --git a/src/libcamera/camera_sensor.cpp b/src/libcamera/camera_sensor.cpp
> index 05a1d7c22e97..f7939b94d2f8 100644
> --- a/src/libcamera/camera_sensor.cpp
> +++ b/src/libcamera/camera_sensor.cpp
> @@ -245,6 +245,7 @@ int CameraSensor::validateSensorDriver()
>  	const std::vector<uint32_t> mandatoryControls{
>  		V4L2_CID_PIXEL_RATE,
>  		V4L2_CID_HBLANK,
> +		V4L2_CID_EXPOSURE,
>  	};
>  
>  	ControlList ctrls = subdev_->getControls(mandatoryControls);

-- 
Regards,

Laurent Pinchart