[PATCH v4 2/3] libcamera: internal: Add MediaPipeline helper
Kieran Bingham
kieran.bingham at ideasonboard.com
Mon Apr 28 16:46:16 CEST 2025
Quoting Paul Elder (2025-04-02 08:39:17)
> From: Kieran Bingham <kieran.bingham at ideasonboard.com>
>
> Provide a MediaPipeline class to help identifing and managing pipelines across
> a MediaDevice graph.
>
> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> Reviewed-by: Umang Jain <umang.jain at ideasonboard.com>
> Reviewed-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>
> Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
> ---
> include/libcamera/internal/media_pipeline.h | 60 ++++
> include/libcamera/internal/meson.build | 1 +
> src/libcamera/media_pipeline.cpp | 302 ++++++++++++++++++++
> src/libcamera/meson.build | 1 +
> 4 files changed, 364 insertions(+)
> create mode 100644 include/libcamera/internal/media_pipeline.h
> create mode 100644 src/libcamera/media_pipeline.cpp
>
> diff --git a/include/libcamera/internal/media_pipeline.h b/include/libcamera/internal/media_pipeline.h
> new file mode 100644
> index 000000000000..b5a224e7172f
> --- /dev/null
> +++ b/include/libcamera/internal/media_pipeline.h
> @@ -0,0 +1,60 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2024, Ideas on Board Oy
> + *
> + * Media pipeline support
> + */
> +
> +#pragma once
> +
> +#include <list>
> +#include <string>
> +
> +#include <libcamera/base/log.h>
> +
> +namespace libcamera {
> +
> +class CameraSensor;
> +class MediaEntity;
> +class MediaLink;
> +class MediaPad;
> +struct V4L2SubdeviceFormat;
> +
> +class MediaPipeline
> +{
> +public:
> + int init(MediaEntity *source, std::string sink);
> + int initLinks();
> + int configure(CameraSensor *sensor, V4L2SubdeviceFormat *);
> +
> +private:
> + struct Entity {
> + /* The media entity, always valid. */
> + MediaEntity *entity;
> + /*
> + * Whether or not the entity is a subdev that supports the
> + * routing API.
> + */
> + bool supportsRouting;
> + /*
> + * The local sink pad connected to the upstream entity, null for
> + * the camera sensor at the beginning of the pipeline.
> + */
> + const MediaPad *sink;
> + /*
> + * The local source pad connected to the downstream entity, null
> + * for the video node at the end of the pipeline.
> + */
> + const MediaPad *source;
> + /*
> + * The link on the source pad, to the downstream entity, null
> + * for the video node at the end of the pipeline.
> + */
> + MediaLink *sourceLink;
> + };
> +
> + std::vector<const MediaPad *> routedSourcePads(MediaPad *sink);
> + std::list<Entity> entities_;
> +};
> +
> +} /* namespace libcamera */
> diff --git a/include/libcamera/internal/meson.build b/include/libcamera/internal/meson.build
> index 45408b313848..33f318b2b602 100644
> --- a/include/libcamera/internal/meson.build
> +++ b/include/libcamera/internal/meson.build
> @@ -32,6 +32,7 @@ libcamera_internal_headers = files([
> 'matrix.h',
> 'media_device.h',
> 'media_object.h',
> + 'media_pipeline.h',
> 'pipeline_handler.h',
> 'process.h',
> 'pub_key.h',
> diff --git a/src/libcamera/media_pipeline.cpp b/src/libcamera/media_pipeline.cpp
> new file mode 100644
> index 000000000000..c9a40e44a81d
> --- /dev/null
> +++ b/src/libcamera/media_pipeline.cpp
> @@ -0,0 +1,302 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2024, Ideas on Board Oy
> + *
> + * Media pipeline support
> + */
> +
> +#include "libcamera/internal/media_pipeline.h"
> +
> +#include <algorithm>
> +#include <errno.h>
> +#include <queue>
> +#include <string>
> +#include <unordered_map>
> +#include <unordered_set>
> +#include <vector>
> +
> +#include <linux/media.h>
> +
> +#include <libcamera/base/log.h>
> +
> +#include "libcamera/internal/camera_sensor.h"
> +#include "libcamera/internal/media_device.h"
> +#include "libcamera/internal/media_object.h"
> +#include "libcamera/internal/v4l2_subdevice.h"
> +
> +/**
> + * \file media_pipeline.h
> + * \brief Provide a representation of a pipeline of devices using the Media
> + * Controller.
> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(MediaPipeline)
> +
> +/**
> + * \class MediaPipeline
> + * \brief The MediaPipeline represents a set of entities that together form a
> + * data path for stream data.
> + *
> + * A MediaPipeline instance is constructed from a sink and a source between
> + * two entities in a media graph.
> + */
> +
> +/**
> + * \brief Retrieve all source pads connected to a sink pad through active routes
> + *
> + * Examine the entity using the V4L2 Subdevice Routing API to collect all the
> + * source pads which are connected with an active route to the sink pad.
> + *
> + * \return A vector of source MediaPads
> + */
> +std::vector<const MediaPad *> MediaPipeline::routedSourcePads(MediaPad *sink)
> +{
> + MediaEntity *entity = sink->entity();
> + std::unique_ptr<V4L2Subdevice> subdev =
> + std::make_unique<V4L2Subdevice>(entity);
> +
> + int ret = subdev->open();
> + if (ret < 0)
> + return {};
> +
> + V4L2Subdevice::Routing routing = {};
> + ret = subdev->getRouting(&routing, V4L2Subdevice::ActiveFormat);
> + if (ret < 0)
> + return {};
> +
> + std::vector<const MediaPad *> pads;
> +
> + for (const V4L2Subdevice::Route &route : routing) {
> + if (sink->index() != route.sink.pad ||
> + !(route.flags & V4L2_SUBDEV_ROUTE_FL_ACTIVE))
> + continue;
> +
> + const MediaPad *pad = entity->getPadByIndex(route.source.pad);
> + if (!pad) {
> + LOG(MediaPipeline, Error)
> + << "Entity " << entity->name()
> + << " has invalid route source pad "
> + << route.source.pad;
> + return {};
> + }
> +
> + pads.push_back(pad);
> + }
> +
> + return pads;
> +}
> +
> +/**
> + * \brief Find the path from source to sink
> + *
> + * Starting from a source entity, determine the shortest path to the target
> + * described by \a sink.
> + *
> + * If \a sink can not be found, or a route from source to sink can not be
> + * achieved an error of -ENOLINK will be returned.
> + *
> + * When successful, the MediaPipeline will internally store the representation
> + * of entities and links to describe the path between the two entities.
> + *
> + * \return 0 on success, a negative errno otherwise
> + */
> +int MediaPipeline::init(MediaEntity *source, std::string sink)
> +{
> + /*
> + * Find the shortest path between from the Camera Sensor and the
> + * target entity.
> + */
> + std::unordered_set<MediaEntity *> visited;
> + std::queue<std::tuple<MediaEntity *, MediaPad *>> queue;
> +
> + /* Remember at each entity where we came from. */
> + std::unordered_map<MediaEntity *, Entity> parents;
> + MediaEntity *entity = nullptr;
> + MediaEntity *target = nullptr;
> + MediaPad *sinkPad;
> +
> + queue.push({ source, nullptr });
> +
> + while (!queue.empty()) {
> + std::tie(entity, sinkPad) = queue.front();
> + queue.pop();
> +
> + /* Found the target device. */
> + if (entity->name() == sink) {
> + LOG(MediaPipeline, Debug)
> + << "Found Pipeline target " << entity->name();
> + target = entity;
> + break;
> + }
> +
> + visited.insert(entity);
> +
> + /*
> + * Add direct downstream entities to the search queue. If the
> + * current entity supports the subdev internal routing API,
> + * restrict the search to downstream entities reachable through
> + * active routes.
> + */
> +
> + std::vector<const MediaPad *> pads;
> + bool supportsRouting = false;
> +
> + if (sinkPad) {
> + pads = routedSourcePads(sinkPad);
> + if (!pads.empty())
> + supportsRouting = true;
> + }
> +
> + if (pads.empty()) {
> + for (const MediaPad *pad : entity->pads()) {
> + if (!(pad->flags() & MEDIA_PAD_FL_SOURCE))
> + continue;
> + pads.push_back(pad);
> + }
> + }
> +
> + for (const MediaPad *pad : pads) {
> + for (MediaLink *link : pad->links()) {
> + MediaEntity *next = link->sink()->entity();
> + if (visited.find(next) == visited.end()) {
> + queue.push({ next, link->sink() });
> +
> + Entity e{ entity, supportsRouting, sinkPad, pad, link };
> + parents.insert({ next, e });
> + }
> + }
> + }
> + }
> +
> + if (!target) {
> + LOG(MediaPipeline, Error) << "Failed to connect " << source->name();
> + return -ENOLINK;
> + }
> +
> + /*
> + * With the parents, we can follow back our way from the capture device
> + * to the sensor. Store all the entities in the pipeline, from the
> + * camera sensor to the video node, in entities_.
> + */
> + entities_.push_front({ entity, false, sinkPad, nullptr, nullptr });
> +
> + for (auto it = parents.find(entity); it != parents.end();
> + it = parents.find(entity)) {
> + const Entity &e = it->second;
> + entities_.push_front(e);
> + entity = e.entity;
> + }
> +
> + LOG(MediaPipeline, Info)
> + << "Found pipeline: "
> + << utils::join(entities_, " -> ",
> + [](const Entity &e) {
> + std::string s = "[";
> + if (e.sink)
> + s += std::to_string(e.sink->index()) + "|";
> + s += e.entity->name();
> + if (e.source)
> + s += "|" + std::to_string(e.source->index());
> + s += "]";
> + return s;
> + });
> +
> + return 0;
> +}
> +
> +/**
> + * \brief Initialise and enable all links through the MediaPipeline
> + * \return 0 on success, or a negative errno otherwise
> + */
> +int MediaPipeline::initLinks()
> +{
> + int ret = 0;
> +
> + MediaLink *sinkLink = nullptr;
> + for (Entity &e : entities_) {
> + /* Sensor entities have no connected sink. */
> + if (!sinkLink) {
> + sinkLink = e.sourceLink;
> + continue;
> + }
> +
> + LOG(MediaPipeline, Debug) << "Enabling : " << *sinkLink;
> +
> + if (!(sinkLink->flags() & MEDIA_LNK_FL_ENABLED)) {
> + ret = sinkLink->setEnabled(true);
> + if (ret < 0)
> + return ret;
> + }
> +
> + sinkLink = e.sourceLink;
> + }
> +
> + return ret;
> +}
> +
> +/**
> + * \brief Configure the entities of this MediaPipeline
> + *
> + * Propagate formats through each of the entities of the Pipeline, validating
> + * that each one was not adjusted by the driver from the desired format.
> + *
> + * \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;
We need to make this *format.
> + return -EINVAL;
> + }
> +
> + LOG(MediaPipeline, Debug)
> + << "Link " << *link << " configured with format "
> + << format;
This too.
> + }
> +
> + return 0;
> +}
> +
> +} /* namespace libcamera */
> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
> index de22b8e60dde..800d408077be 100644
> --- a/src/libcamera/meson.build
> +++ b/src/libcamera/meson.build
> @@ -43,6 +43,7 @@ libcamera_internal_sources = files([
> 'matrix.cpp',
> 'media_device.cpp',
> 'media_object.cpp',
> + 'media_pipeline.cpp',
> 'pipeline_handler.cpp',
> 'process.cpp',
> 'pub_key.cpp',
> --
> 2.47.2
>
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