/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2019, Google Inc.
 *
 * v4l2_videodevice.cpp - V4L2 Video Device
 */

#include "libcamera/internal/v4l2_videodevice.h"

#include <fcntl.h>
#include <iomanip>
#include <sstream>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <unistd.h>
#include <vector>

#include <linux/version.h>

#include <libcamera/event_notifier.h>
#include <libcamera/file_descriptor.h>

#include "libcamera/internal/log.h"
#include "libcamera/internal/media_device.h"
#include "libcamera/internal/media_object.h"
#include "libcamera/internal/utils.h"

/**
 * \file v4l2_videodevice.h
 * \brief V4L2 Video Device
 */
namespace libcamera {

LOG_DECLARE_CATEGORY(V4L2)

/**
 * \struct V4L2Capability
 * \brief struct v4l2_capability object wrapper and helpers
 *
 * The V4L2Capability structure manages the information returned by the
 * VIDIOC_QUERYCAP ioctl.
 */

/**
 * \fn V4L2Capability::driver()
 * \brief Retrieve the driver module name
 * \return The string containing the name of the driver module
 */

/**
 * \fn V4L2Capability::card()
 * \brief Retrieve the video device card name
 * \return The string containing the video device name
 */

/**
 * \fn V4L2Capability::bus_info()
 * \brief Retrieve the location of the video device in the system
 * \return The string containing the video device location
 */

/**
 * \fn V4L2Capability::device_caps()
 * \brief Retrieve the capabilities of the video device
 * \return The video device specific capabilities if V4L2_CAP_DEVICE_CAPS is
 * set or driver capabilities otherwise
 */

/**
 * \fn V4L2Capability::isMultiplanar()
 * \brief Identify if the video device implements the V4L2 multiplanar APIs
 * \return True if the video device supports multiplanar APIs
 */

/**
 * \fn V4L2Capability::isCapture()
 * \brief Identify if the video device captures data
 * \return True if the video device can capture data
 */

/**
 * \fn V4L2Capability::isOutput()
 * \brief Identify if the video device outputs data
 * \return True if the video device can output data
 */

/**
 * \fn V4L2Capability::isVideo()
 * \brief Identify if the video device captures or outputs images
 * \return True if the video device can capture or output images
 */

/**
 * \fn V4L2Capability::isM2M()
 * \brief Identify if the device is a Memory-to-Memory device
 * \return True if the device can capture and output images using the M2M API
 */

/**
 * \fn V4L2Capability::isMeta()
 * \brief Identify if the video device captures or outputs image meta-data
 * \return True if the video device can capture or output image meta-data
 */

/**
 * \fn V4L2Capability::isVideoCapture()
 * \brief Identify if the video device captures images
 * \return True if the video device can capture images
 */

/**
 * \fn V4L2Capability::isVideoOutput()
 * \brief Identify if the video device outputs images
 * \return True if the video device can output images
 */

/**
 * \fn V4L2Capability::isMetaCapture()
 * \brief Identify if the video device captures image meta-data
 * \return True if the video device can capture image meta-data
 */

/**
 * \fn V4L2Capability::isMetaOutput()
 * \brief Identify if the video device outputs image meta-data
 * \return True if the video device can output image meta-data
 */

/**
 * \fn V4L2Capability::hasStreaming()
 * \brief Determine if the video device can perform Streaming I/O
 * \return True if the video device provides Streaming I/O IOCTLs
 */

/**
 * \class V4L2BufferCache
 * \brief Hot cache of associations between V4L2 buffer indexes and FrameBuffer
 *
 * When importing buffers, V4L2 performs lazy mapping of dmabuf instances at
 * VIDIOC_QBUF (or VIDIOC_PREPARE_BUF) time and keeps the mapping associated
 * with the V4L2 buffer, as identified by its index. If the same V4L2 buffer is
 * then reused and queued with different dmabufs, the old dmabufs will be
 * unmapped and the new ones mapped. To keep this process efficient, it is
 * crucial to consistently use the same V4L2 buffer for given dmabufs through
 * the whole duration of a capture cycle.
 *
 * The V4L2BufferCache class keeps a map of previous dmabufs to V4L2 buffer
 * index associations to help selecting V4L2 buffers. It tracks, for every
 * entry, if the V4L2 buffer is in use, and offers lookup of the best free V4L2
 * buffer for a set of dmabufs.
 */

/**
 * \brief Create an empty cache with \a numEntries entries
 * \param[in] numEntries Number of entries to reserve in the cache
 *
 * Create a cache with \a numEntries entries all marked as unused. The entries
 * will be populated as the cache is used. This is typically used to implement
 * buffer import, with buffers added to the cache as they are queued.
 */
V4L2BufferCache::V4L2BufferCache(unsigned int numEntries)
	: lastUsedCounter_(1), missCounter_(0)
{
	cache_.resize(numEntries);
}

/**
 * \brief Create a pre-populated cache
 * \param[in] buffers Array of buffers to pre-populated with
 *
 * Create a cache pre-populated with \a buffers. This is typically used to
 * implement buffer export, with all buffers added to the cache when they are
 * allocated.
 */
V4L2BufferCache::V4L2BufferCache(const std::vector<std::unique_ptr<FrameBuffer>> &buffers)
	: lastUsedCounter_(1), missCounter_(0)
{
	for (const std::unique_ptr<FrameBuffer> &buffer : buffers)
		cache_.emplace_back(true,
				    lastUsedCounter_.fetch_add(1, std::memory_order_acq_rel),
				    buffer->planes());
}

V4L2BufferCache::~V4L2BufferCache()
{
	if (missCounter_ > cache_.size())
		LOG(V4L2, Debug) << "Cache misses: " << missCounter_;
}

/**
 * \brief Find the best V4L2 buffer for a FrameBuffer
 * \param[in] buffer The FrameBuffer
 *
 * Find the best V4L2 buffer index to be used for the FrameBuffer \a buffer
 * based on previous mappings of frame buffers to V4L2 buffers. If a free V4L2
 * buffer previously used with the same dmabufs as \a buffer is found in the
 * cache, return its index. Otherwise return the index of the first free V4L2
 * buffer and record its association with the dmabufs of \a buffer.
 *
 * \return The index of the best V4L2 buffer, or -ENOENT if no free V4L2 buffer
 * is available
 */
int V4L2BufferCache::get(const FrameBuffer &buffer)
{
	bool hit = false;
	int use = -1;
	uint64_t oldest = UINT64_MAX;

	for (unsigned int index = 0; index < cache_.size(); index++) {
		const Entry &entry = cache_[index];

		if (!entry.free)
			continue;