LICENSES/BSD-2-Clause.txt


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Copyright (c) <year> <owner>. All rights reserved.

Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2018, Google Inc.
 *
 * media_device.cpp - Media device handler
 */

#include "libcamera/internal/media_device.h"

#include <errno.h>
#include <fcntl.h>
#include <stdint.h>
#include <string>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <vector>

#include <linux/media.h>

#include <libcamera/base/log.h>

/**
 * \file media_device.h
 * \brief Provide a representation of a Linux kernel Media Controller device
 * that exposes the full graph topology.
 */

namespace libcamera {

LOG_DEFINE_CATEGORY(MediaDevice)

/**
 * \class MediaDevice
 * \brief The MediaDevice represents a Media Controller device with its full
 * graph of connected objects.
 *
 * A MediaDevice instance is associated with a media controller device node when
 * created, and that association is kept for the lifetime of the MediaDevice
 * instance.
 *
 * The instance is created with an empty media graph. Before performing any
 * other operation, it must be populate by calling populate(). Instances of
 * MediaEntity, MediaPad and MediaLink are created to model the media graph,
 * and stored in a map indexed by object id.
 *
 * The graph is valid once successfully populated, as reported by the isValid()
 * function. It can be queried to list all entities(), or entities can be
 * looked up by name with getEntityByName(). The graph can be traversed from
 * entity to entity through pads and links as exposed by the corresponding
 * classes.
 *
 * Media devices can be claimed for exclusive use with acquire(), released with
 * release() and tested with busy(). This mechanism is aimed at pipeline
 * managers to claim media devices they support during enumeration.
 */

/**
 * \brief Construct a MediaDevice
 * \param[in] deviceNode The media device node path
 *
 * Once constructed the media device is invalid, and must be populated with
 * populate() before the media graph can be queried.
 */
MediaDevice::MediaDevice(const std::string &deviceNode)
	: deviceNode_(deviceNode), valid_(false), acquired_(false)
{
}

MediaDevice::~MediaDevice()
{
	fd_.reset();
	clear();
}

std::string MediaDevice::logPrefix() const
{
	return deviceNode() + "[" + driver() + "]";
}

/**
 * \brief Claim a device for exclusive use
 *
 * The device claiming mechanism offers simple media device access arbitration
 * between multiple users. When the media device is created, it is available to
 * all users. Users can query the media graph to determine whether they can
 * support the device and, if they do, claim the device for exclusive use. Other
 * users are then expected to skip over media devices in use as reported by the
 * busy() function.
 *
 * Once claimed the device shall be released by its user when not needed anymore
 * by calling the release() function. Acquiring the media device opens a file
 * descriptor to the device which is kept open until release() is called.
 *
 * Exclusive access is only guaranteed if all users of the media device abide by
 * the device claiming mechanism, as it isn't enforced by the media device
 * itself.
 *
 * \return true if the device was successfully claimed, or false if it was
 * already in use
 * \sa release(), busy()
 */
bool MediaDevice::acquire()
{
	if (acquired_)
		return false;

	if (open())
		return false;

	acquired_ = true;
	return true;
}

/**
 * \brief Release a device previously claimed for exclusive use
 * \sa acquire(), busy()
 */
void MediaDevice::release()
{
	close();
	acquired_ = false;
}

/**
 * \brief Lock the device to prevent it from being used by other instances of
 * libcamera
 *
 * Multiple instances of libcamera might be running on the same system, at the
 * same time. To allow the different instances to coexist, system resources in
 * the form of media devices must be accessible for enumerating the cameras
 * they provide at all times, while still allowing an instance to lock a
 * resource while it prepares to actively use a camera from the resource.
 *
 * This function shall not be called from a pipeline handler implementation
 * directly, as the base PipelineHandler implementation handles this on the
 * behalf of the specified implementation.
 *
 * \return True if the device could be locked, false otherwise
 * \sa unlock()
 */
bool MediaDevice::lock()
{
	if (!fd_.isValid())
		return false;

	if (lockf(fd_.get(), F_TLOCK, 0))
		return false;

	return true;
}

/**
 * \brief Unlock the device and free it for use for libcamera instances
 *
 * This function shall not be called from a pipeline handler implementation
 * directly, as the base PipelineHandler implementation handles this on the
 * behalf of the specified implementation.
 *
 * \sa lock()
 */
void MediaDevice::unlock()
{
	if (!fd_.isValid())
		return;

	lockf(fd_.get(), F_ULOCK, 0);
}

/**
 * \fn MediaDevice::busy()
 * \brief Check if a device is in use
 * \return true if the device has been claimed for exclusive use, or false if it
 * is available
 * \sa acquire(), release()
 */

/**
 * \brief Populate the MediaDevice with device information and media objects
 *
 * This function retrieves the media device information and enumerates all
 * media objects in the media device graph and creates their MediaObject
 * representations. All entities, pads and links are stored as MediaEntity,
 * MediaPad and MediaLink respectively, with cross-references between objects.
 * Interfaces are not processed.
 *
 * Entities are stored in a separate list in the MediaDevice to ease lookup,
 * while pads are accessible from the entity they belong to and links from the
 * pads they connect.
 *
 * \return 0 on success or a negative error code otherwise
 */
int MediaDevice::populate()
{
	struct media_v2_topology topology = {};
	struct media_v2_entity *ents = nullptr;
	struct media_v2_interface *interfaces = nullptr;
	struct media_v2_link *links = nullptr;
	struct media_v2_pad *pads = nullptr;
	__u64 version = -1;
	int ret;

	clear();

	ret = open();
	if (ret)
		return ret;

	struct media_device_info info = {};
	ret = ioctl(fd_.get(), MEDIA_IOC_DEVICE_INFO, &info);
	if (ret) {
		ret = -errno;
		LOG(MediaDevice, Error)
			<< "Failed to get media device info " << strerror(-ret);
		goto done;
	}

	driver_ = info.driver;
	model_ = info.model;
	version_ = info.media_version;
	hwRevision_ = info.hw_revision;

	/*
	 * Keep calling G_TOPOLOGY until the version number stays stable.
	 */
	while (true) {
		topology.topology_version = 0;
		topology.ptr_entities = reinterpret_cast<uintptr_t>(ents);
		topology.ptr_interfaces = reinterpret_cast<uintptr_t>(interfaces);
		topology.ptr_links = reinterpret_cast<uintptr_t>(links);
		topology.ptr_pads = reinterpret_cast<uintptr_t>(pads);

		ret = ioctl(fd_.get(), MEDIA_IOC_G_TOPOLOGY, &topology);
		if (ret < 0) {
			ret = -errno;
			LOG(MediaDevice, Error)
				<< "Failed to enumerate topology: "
				<< strerror(-ret);
			goto done;
		}

		if (version == topology.topology_version)
			break;

		delete[] ents;
		delete[] interfaces;
		delete[] pads;
		delete[] links;

		ents = new struct media_v2_entity[topology.num_entities]();
		interfaces = new struct media_v2_interface[topology.num_interfaces]();
		links = new struct media_v2_link[topology.num_links]();
		pads = new struct media_v2_pad[topology.num_pads]();

		version = topology.topology_version;
	}

	/* Populate entities, pads and links. */
	if (populateEntities(topology) &&
	    populatePads(topology) &&
	    populateLinks(topology))
		valid_ = true;

	ret = 0;
done:
	close();

	delete[] ents;
	delete[] interfaces;
	delete[] pads;
	delete[] links;

	if (!valid_) {
		clear();
		return -EINVAL;
	}

	return ret;
}

/**
 * \fn MediaDevice::isValid()
 * \brief Query whether the media graph has been populated and is valid
 * \return true if the media graph is valid, false otherwise
 */

/**
 * \fn MediaDevice::driver()
 * \brief Retrieve the media device driver name
 * \return The name of the kernel driver that handles the MediaDevice
 */

/**
 * \fn MediaDevice::deviceNode()
 * \brief Retrieve the media device node path
 * \return The MediaDevice deviceNode path
 */

/**
 * \fn MediaDevice::model()
 * \brief Retrieve the media device model name
 * \return The MediaDevice model name
 */

/**
 * \fn MediaDevice::version()
 * \brief Retrieve the media device API version
 *
 * The version is formatted with the KERNEL_VERSION() macro.
 *
 * \return The MediaDevice API version
 */

/**
 * \fn MediaDevice::hwRevision()
 * \brief Retrieve the media device hardware revision
 *
 * The hardware revision is in a driver-specific format.
 *
 * \return The MediaDevice hardware revision
 */

/**
 * \fn MediaDevice::entities()
 * \brief Retrieve the list of entities in the media graph
 * \return The list of MediaEntities registered in the MediaDevice
 */

/**
 * \brief Return the MediaEntity with name \a name
 * \param[in] name The entity name
 * \return The entity with \a name, or nullptr if no such entity is found
 */
MediaEntity *MediaDevice::getEntityByName(const std::string &name) const
{
	for (MediaEntity *e : entities_)
		if (e->name() == name)
			return e;

	return nullptr;
}

/**
 * \brief Retrieve the MediaLink connecting two pads, identified by entity
 * names and pad indexes
 * \param[in] sourceName The source entity name
 * \param[in] sourceIdx The index of the source pad
 * \param[in] sinkName The sink entity name
 * \param[in] sinkIdx The index of the sink pad
 *
 * Find the link that connects the pads at index \a sourceIdx of the source
 * entity with name \a sourceName, to the pad at index \a sinkIdx of the
 * sink entity with name \a sinkName, if any.
 *
 * \sa MediaDevice::link(const MediaEntity *source, unsigned int sourceIdx, const MediaEntity *sink, unsigned int sinkIdx) const
 * \sa MediaDevice::link(const MediaPad *source, const MediaPad *sink) const
 *
 * \return The link that connects the two pads, or nullptr if no such a link
 * exists
 */
MediaLink *MediaDevice::link(const std::string &sourceName, unsigned int sourceIdx,
			     const std::string &sinkName, unsigned int sinkIdx)
{
	const MediaEntity *source = getEntityByName(sourceName);
	const MediaEntity *sink = getEntityByName(sinkName);
	if (!source || !sink)
		return nullptr;

	return link(source, sourceIdx, sink, sinkIdx);
}

/**
 * \brief Retrieve the MediaLink connecting two pads, identified by the
 * entities they belong to and pad indexes
 * \param[in] source The source entity
 * \param[in] sourceIdx The index of the source pad
 * \param[in] sink The sink entity
 * \param[in] sinkIdx The index of the sink pad
 *
 * Find the link that connects the pads at index \a sourceIdx of the source
 * entity \a source, to the pad at index \a sinkIdx of the sink entity \a
 * sink, if any.
 *
 * \sa MediaDevice::link(const std::string &sourceName, unsigned int sourceIdx, const std::string &sinkName, unsigned int sinkIdx) const
 * \sa MediaDevice::link(const MediaPad *source, const MediaPad *sink) const
 *
 * \return The link that connects the two pads, or nullptr if no such a link
 * exists
 */
MediaLink *MediaDevice::link(const MediaEntity *source, unsigned int sourceIdx,
			     const MediaEntity *sink, unsigned int sinkIdx)
{

	const MediaPad *sourcePad = source->getPadByIndex(sourceIdx);
	const MediaPad *sinkPad = sink->getPadByIndex(sinkIdx);
	if (!sourcePad || !sinkPad)
		return nullptr;

	return link(sourcePad, sinkPad);
}

/**
 * \brief Retrieve the MediaLink that connects two pads
 * \param[in] source The source pad
 * \param[in] sink The sink pad
 *
 * \sa MediaDevice::link(const std::string &sourceName, unsigned int sourceIdx, const std::string &sinkName, unsigned int sinkIdx) const
 * \sa MediaDevice::link(const MediaEntity *source, unsigned int sourceIdx, const MediaEntity *sink, unsigned int sinkIdx) const
 *
 * \return The link that connects the two pads, or nullptr if no such a link
 * exists
 */
MediaLink *MediaDevice::link(const MediaPad *source, const MediaPad *sink)
{
	for (MediaLink *link : source->links()) {
		if (link->sink()->id() == sink->id())
			return link;
	}

	return nullptr;
}

/**
 * \brief Disable all links in the media device
 *
 * Disable all the media device links, clearing the MEDIA_LNK_FL_ENABLED flag
 * on links which are not flagged as IMMUTABLE.
 *
 * \return 0 on success or a negative error code otherwise
 */
int MediaDevice::disableLinks()
{
	for (MediaEntity *entity : entities_) {
		for (MediaPad *pad : entity->pads()) {
			if (!(pad->flags() & MEDIA_PAD_FL_SOURCE))
				continue;

			for (MediaLink *link : pad->links()) {
				if (link->flags() & MEDIA_LNK_FL_IMMUTABLE)
					continue;

				int ret = link->setEnabled(false);
				if (ret)
					return ret;
			}
		}
	}

	return 0;
}

/**
 * \var MediaDevice::disconnected
 * \brief Signal emitted when the media device is disconnected from the system
 *
 * This signal is emitted when the device enumerator detects that the media
 * device has been removed from the system. For hot-pluggable devices this is
 * usually caused by physical device disconnection, but can also result from
 * driver unloading for most devices. The media device is passed as a parameter.
 */

/**
 * \brief Open the media device
 *
 * \return 0 on success or a negative error code otherwise
 * \retval -EBUSY Media device already open
 * \sa close()
 */
int MediaDevice::open()
{
	if (fd_.isValid()) {
		LOG(MediaDevice, Error) << "MediaDevice already open";
		return -EBUSY;
	}

	fd_ = UniqueFD(::open(deviceNode_.c_str(), O_RDWR));
	if (!fd_.isValid()) {
		int ret = -errno;
		LOG(MediaDevice, Error)
			<< "Failed to open media device at "
			<< deviceNode_ << ": " << strerror(-ret);
		return ret;
	}

	return 0;
}

/**
 * \brief Close the media device
 *
 * This function closes the media device node. It does not invalidate the media
 * graph and all cached media objects remain valid and can be accessed normally.
 * Once closed no operation interacting with the media device node can be
 * performed until the device is opened again.
 *
 * Closing an already closed device is allowed and will not perform any
 * operation.
 *
 * \sa open()
 */
void MediaDevice::close()
{
	fd_.reset();
}

/**
 * \var MediaDevice::objects_
 * \brief Global map of media objects (entities, pads, links) keyed by their
 * object id.
 */

/**
 * \brief Retrieve the media graph object specified by \a id
 * \return The graph object, or nullptr if no object with \a id is found
 */
MediaObject *MediaDevice::object(unsigned int id)
{
	auto it = objects_.find(id);
	return (it == objects_.end()) ? nullptr : it->second;
}

/**
 * \brief Add a media object to the media graph
 *
 * If the \a object has a unique id it is added to the media graph, and its
 * lifetime will be managed by the media device. Otherwise the object isn't
 * added to the graph and the caller must delete it.
 *
 * \return true if the object was successfully added to the graph and false
 * otherwise
 */
bool MediaDevice::addObject(MediaObject *object)
{

	if (objects_.find(object->id()) != objects_.end()) {
		LOG(MediaDevice, Error)
			<< "Element with id " << object->id()
			<< " already enumerated.";
		return false;
	}

	objects_[object->id()] = object;

	return true;
}

/**
 * \brief Delete all graph objects in the media device
 *
 * Clear the media graph and delete all the objects it contains. After this
 * function returns any previously obtained pointer to a media graph object
 * becomes invalid.
 *
 * The media device graph state is reset to invalid when the graph is cleared.
 *
 * \sa isValid()
 */
void MediaDevice::clear()
{
	for (auto const &o : objects_)
		delete o.second;

	objects_.clear();
	entities_.clear();
	valid_ = false;
}

/**
 * \var MediaDevice::entities_
 * \brief Global list of media entities in the media graph
 */

/**
 * \brief Find the interface associated with an entity
 * \param[in] topology The media topology as returned by MEDIA_IOC_G_TOPOLOGY
 * \param[in] entityId The entity id
 * \return A pointer to the interface if found, or nullptr otherwise
 */
struct media_v2_interface *MediaDevice::findInterface(const struct media_v2_topology &topology,
						      unsigned int entityId)
{
	struct media_v2_link *links = reinterpret_cast<struct media_v2_link *>
						      (topology.ptr_links);
	unsigned int ifaceId = 0;
	unsigned int i;

	for (i = 0; i < topology.num_links; ++i) {
		/* Search for the interface to entity link. */
		if (links[i].sink_id != entityId)
			continue;

		if ((links[i].flags & MEDIA_LNK_FL_LINK_TYPE) !=
		    MEDIA_LNK_FL_INTERFACE_LINK)
			continue;

		ifaceId = links[i].source_id;
		break;
	}
	if (i == topology.num_links)
		return nullptr;

	struct media_v2_interface *ifaces = reinterpret_cast<struct media_v2_interface *>
					    (topology.ptr_interfaces);
	for (i = 0; i < topology.num_interfaces; ++i) {
		if (ifaces[i].id == ifaceId)
			return &ifaces[i];
	}

	return nullptr;
}

/*
 * For each entity in the media graph create a MediaEntity and store a
 * reference in the media device objects map and entities list.
 */
bool MediaDevice::populateEntities(const struct media_v2_topology &topology)
{
	struct media_v2_entity *mediaEntities = reinterpret_cast<struct media_v2_entity *>
						(topology.ptr_entities);

	for (unsigned int i = 0; i < topology.num_entities; ++i) {
		struct media_v2_entity *ent = &mediaEntities[i];

		/*
		 * The media_v2_entity structure was missing the flag field before
		 * v4.19.
		 */
		if (!MEDIA_V2_ENTITY_HAS_FLAGS(version_))
			fixupEntityFlags(ent);

		/*
		 * Find the interface linked to this entity to get the device
		 * node major and minor numbers.
		 */
		struct media_v2_interface *iface =
			findInterface(topology, ent->id);
		MediaEntity *entity = new MediaEntity(this, ent, iface);

		if (!addObject(entity)) {
			delete entity;
			return false;
		}

		entities_.push_back(entity);
	}

	return true;
}

bool MediaDevice::populatePads(const struct media_v2_topology &topology)
{
	struct media_v2_pad *mediaPads = reinterpret_cast<struct media_v2_pad *>
					 (topology.ptr_pads);

	for (unsigned int i = 0; i < topology.num_pads; ++i) {
		unsigned int entity_id = mediaPads[i].entity_id;

		/* Store a reference to this MediaPad in entity. */
		MediaEntity *mediaEntity = dynamic_cast<MediaEntity *>
					   (object(entity_id));
		if (!mediaEntity) {
			LOG(MediaDevice, Error)
				<< "Failed to find entity with id: "
				<< entity_id;
			return false;
		}

		MediaPad *pad = new MediaPad(&mediaPads[i], mediaEntity);
		if (!addObject(pad)) {
			delete pad;
			return false;
		}

		mediaEntity->addPad(pad);
	}

	return true;
}

bool MediaDevice::populateLinks(const struct media_v2_topology &topology)
{
	struct media_v2_link *mediaLinks = reinterpret_cast<struct media_v2_link *>
					   (topology.ptr_links);

	for (unsigned int i = 0; i < topology.num_links; ++i) {
		if ((mediaLinks[i].flags & MEDIA_LNK_FL_LINK_TYPE) ==
		    MEDIA_LNK_FL_INTERFACE_LINK)
			continue;

		/* Look up the source and sink objects. */
		unsigned int source_id = mediaLinks[i].source_id;
		MediaObject *source = object(source_id);
		if (!source) {
			LOG(MediaDevice, Error)
				<< "Failed to find MediaObject with id "
				<< source_id;
			return false;
		}

		unsigned int sink_id = mediaLinks[i].sink_id;
		MediaObject *sink = object(sink_id);
		if (!sink) {
			LOG(MediaDevice, Error)
				<< "Failed to find MediaObject with id "
				<< sink_id;
			return false;
		}

		switch (mediaLinks[i].flags & MEDIA_LNK_FL_LINK_TYPE) {
		case MEDIA_LNK_FL_DATA_LINK: {
			MediaPad *sourcePad = dynamic_cast<MediaPad *>(source);
			MediaPad *sinkPad = dynamic_cast<MediaPad *>(sink);
			if (!source || !sink) {
				LOG(MediaDevice, Error)
					<< "Source or sink is not a pad";
				return false;
			}

			MediaLink *link = new MediaLink(&mediaLinks[i],
							sourcePad, sinkPad);
			if (!addObject(link)) {
				delete link;
				return false;
			}

			link->source()->addLink(link);
			link->sink()->addLink(link);

			break;
		}

		case MEDIA_LNK_FL_ANCILLARY_LINK: {
			MediaEntity *primary = dynamic_cast<MediaEntity *>(source);
			MediaEntity *ancillary = dynamic_cast<MediaEntity *>(sink);
			if (!primary || !ancillary) {
				LOG(MediaDevice, Error)
					<< "Source or sink is not an entity";
				return false;
			}

			primary->addAncillaryEntity(ancillary);

			break;
		}

		default:
			LOG(MediaDevice, Warning)
				<< "Unknown media link type";

			break;
		}
	}

	return true;
}

/**
 * \brief Fixup entity flags using the legacy API
 * \param[in] entity The entity
 *
 * This function is used as a fallback to query entity flags using the legacy
 * MEDIA_IOC_ENUM_ENTITIES ioctl when running on a kernel version that doesn't
 * provide them through the MEDIA_IOC_G_TOPOLOGY ioctl.
 */
void MediaDevice::fixupEntityFlags(struct media_v2_entity *entity)
{
	struct media_entity_desc desc = {};
	desc.id = entity->id;

	int ret = ioctl(fd_.get(), MEDIA_IOC_ENUM_ENTITIES, &desc);
	if (ret < 0) {
		ret = -errno;
		LOG(MediaDevice, Debug)
			<< "Failed to retrieve information for entity "
			<< entity->id << ": " << strerror(-ret);
		return;
	}

	entity->flags = desc.flags;
}

/**
 * \brief Apply \a flags to a link between two pads
 * \param[in] link The link to apply flags to
 * \param[in] flags The flags to apply to the link
 *
 * This function applies the link \a flags (as defined by the MEDIA_LNK_FL_*
 * macros from the Media Controller API) to the given \a link. It implements
 * low-level link setup as it performs no checks on the validity of the \a
 * flags, and assumes that the supplied \a flags are valid for the link (e.g.
 * immutable links cannot be disabled).
*
 * \sa MediaLink::setEnabled(bool enable)
 *
 * \return 0 on success or a negative error code otherwise
 */
int MediaDevice::setupLink(const MediaLink *link, unsigned int flags)
{
	struct media_link_desc linkDesc = {};
	MediaPad *source = link->source();
	MediaPad *sink = link->sink();

	linkDesc.source.entity = source->entity()->id();
	linkDesc.source.index = source->index();
	linkDesc.source.flags = MEDIA_PAD_FL_SOURCE;

	linkDesc.sink.entity = sink->entity()->id();
	linkDesc.sink.index = sink->index();
	linkDesc.sink.flags = MEDIA_PAD_FL_SINK;

	linkDesc.flags = flags;

	int ret = ioctl(fd_.get(), MEDIA_IOC_SETUP_LINK, &linkDesc);
	if (ret) {
		ret = -errno;
		LOG(MediaDevice, Error)
			<< "Failed to setup link "
			<< source->entity()->name() << "["
			<< source->index() << "] -> "
			<< sink->entity()->name() << "["
			<< sink->index() << "]: "
			<< strerror(-ret);
		return ret;
	}

	LOG(MediaDevice, Debug)
		<< source->entity()->name() << "["
		<< source->index() << "] -> "