[PATCH v2 3/4] libcamera: internal: Add MediaPipeline helper

[Kieran Bingham]

Quoting Kieran Bingham (2024-10-02 22:26:31)
> Provide a MediaPipeline class to help identifing and managing pipelines across
> a MediaDevice graph.
> 
> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> 
> ---
> v2:
> 
> - use srcPads to clearly identify which pads are managed
> - Only report enabling links when a change is made
> 
>  - fix header includes
> 
> - Fix includes
> - Remove period at end of briefs
> 
> - Document function parameters
> - expand documentation throughout
> - Fix debug log capitalisation
> 
> - reduce scope of single use 'ret'
> 
> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

... snippity ...

> +
> +/**
> + * \brief Configure the entities of this MediaPipeline
> + * \param[in] sensor The configured CameraSensor to propogate

How did I miss that.

Will add

 * \param[inout] format The format to propogate through the pipeline

> + *
> + * Propagate formats through each of the entities of the Pipeline, validating
> + * that each one was not adjusted by the driver from the desired format.
> + *

Maybe I should add 

 * The format is updated with the final accepted format of the last
 * entity of the pipeline.

> + * \return 0 on success or a negative errno otherwise
> + */
> +int MediaPipeline::configure(CameraSensor *sensor, V4L2SubdeviceFormat *format)
> +{
> +       int ret;
> +
> +       for (const Entity &e : entities_) {
> +               /* The sensor is configured through the CameraSensor */
> +               if (!e.sourceLink)
> +                       break;
> +
> +               MediaLink *link = e.sourceLink;
> +               MediaPad *source = link->source();
> +               MediaPad *sink = link->sink();
> +
> +               /* 'format' already contains the sensor configuration */
> +               if (source->entity() != sensor->entity()) {
> +                       /* todo: Add MediaDevice cache to reduce FD pressure */
> +                       V4L2Subdevice subdev(source->entity());
> +                       ret = subdev.open();
> +                       if (ret)
> +                               return ret;
> +
> +                       ret = subdev.getFormat(source->index(), format);
> +                       if (ret < 0)
> +                               return ret;
> +               }
> +
> +               V4L2SubdeviceFormat sourceFormat = *format;
> +               /* todo: Add MediaDevice cache to reduce FD pressure */
> +               V4L2Subdevice subdev(sink->entity());
> +               ret = subdev.open();
> +               if (ret)
> +                       return ret;
> +
> +               ret = subdev.setFormat(sink->index(), format);
> +               if (ret < 0)
> +                       return ret;
> +
> +               if (format->code != sourceFormat.code ||
> +                   format->size != sourceFormat.size) {
> +                       LOG(MediaPipeline, Debug)
> +                               << "Source '" << *source
> +                               << " produces " << sourceFormat
> +                               << ", sink '" << *sink
> +                               << " requires " << format;
> +                       return -EINVAL;
> +               }
> +
> +               LOG(MediaPipeline, Debug)
> +                       << "Link " << *link << " configured with format "
> +                       << format;
> +       }
> +
> +       return 0;
> +}
> +
> +} /* namespace libcamera */
> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
> index aa9ab0291854..2c0f8603b231 100644
> --- a/src/libcamera/meson.build
> +++ b/src/libcamera/meson.build
> @@ -41,6 +41,7 @@ libcamera_internal_sources = files([
>      'mapped_framebuffer.cpp',
>      'media_device.cpp',
>      'media_object.cpp',
> +    'media_pipeline.cpp',
>      'pipeline_handler.cpp',
>      'process.cpp',
>      'pub_key.cpp',
> -- 
> 2.34.1
>