fc_queue.h

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2022, Google Inc.
 *
 * IPA Frame context queue
 */

#pragma once

#include <stdint.h>
#include <vector>

#include <libcamera/base/log.h>

namespace libcamera {

LOG_DECLARE_CATEGORY(FCQueue)

namespace ipa {

template<typename FrameContext>
class FCQueue;

struct FrameContext {
private:
    template<typename T> friend class FCQueue;
    uint32_t frame;
};

template<typename FrameContext>
class FCQueue
{
public:
    FCQueue(unsigned int size)
        : contexts_(size)
    {
    }

    void clear()
    {
        for (FrameContext &ctx : contexts_)
            ctx.frame = 0;
    }

    FrameContext &alloc(const uint32_t frame)
    {
        FrameContext &frameContext = contexts_[frame % contexts_.size()];

        /*
         * Do not re-initialise if a get() call has already fetched this
         * frame context to preseve the context.
         *
         * \todo If the the sequence number of the context to initialise
         * is smaller than the sequence number of the queue slot to use,
         * it means that we had a serious request underrun and more
         * frames than the queue size has been produced since the last
         * time the application has queued a request. Does this deserve
         * an error condition ?
         */
        if (frame != 0 && frame <= frameContext.frame)
            LOG(FCQueue, Warning)
                << "Frame " << frame << " already initialised";
        else
            init(frameContext, frame);

        return frameContext;
    }

    FrameContext &get(uint32_t frame)
    {
        FrameContext &frameContext = contexts_[frame % contexts_.size()];

        /*
         * If the IPA algorithms try to access a frame context slot which
         * has been already overwritten by a newer context, it means the
         * frame context queue has overflowed and the desired context
         * has been forever lost. The pipeline handler shall avoid
         * queueing more requests to the IPA than the frame context
         * queue size.
         */
        if (frame < frameContext.frame)
            LOG(FCQueue, Fatal) << "Frame context for " << frame
                        << " has been overwritten by "
                        << frameContext.frame;

        if (frame == frameContext.frame)
            return frameContext;

        /*
         * The frame context has been retrieved before it was
         * initialised through the initialise() call. This indicates an
         * algorithm attempted to access a Frame context before it was
         * queued to the IPA. Controls applied for this request may be
         * left unhandled.
         *
         * \todo Set an error flag for per-frame control errors.
         */
        LOG(FCQueue, Warning)
            << "Obtained an uninitialised FrameContext for " << frame;

        init(frameContext, frame);

        return frameContext;
    }

private:
    void init(FrameContext &frameContext, const uint32_t frame)
    {
        frameContext = {};
        frameContext.frame = frame;
    }

    std::vector<FrameContext> contexts_;
};

} /* namespace ipa */

} /* namespace libcamera */