src/libcamera/media_device.cpp


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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2018, Google Inc.
 *
 * media_device.cpp - Media device handler
 */

#include "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 "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 valid()
 * 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 device 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), fd_(-1), valid_(false), acquired_(false),
	  lockOwner_(false)
{
}

MediaDevice::~MediaDevice()
{
	if (fd_ != -1)
		::close(fd_);
	clear();
}

/**
 * \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 method 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_ == -1)
		return false;

	/* Do not allow nested locking in the same libcamera instance. */
	if (lockOwner_)
		return false;

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

	lockOwner_ = true;

	return true;
}

/**
 * \brief Unlock the device and free it for use for libcamera instances
 *
 * This method 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_ == -1)
		return;

	if (!lockOwner_)
		return;

	lockOwner_ = false;

	lockf(fd_, 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_, 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;

	/*
	 * 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_, 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::valid()
 * \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::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_ != -1) {
		LOG(MediaDevice, Error) << "MediaDevice already open";
		return -EBUSY;
	}

	int ret = ::open(deviceNode_.c_str(), O_RDWR);