system/dev/bus/virtio/console.h

// Copyright 2016 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#pragma once

#include "device.h"
#include "ring.h"

#include <ddk/device.h>
#include <fbl/array.h>
#include <fbl/intrusive_double_list.h>
#include <zircon/thread_annotations.h>

namespace virtio {

// Describes a chunk of memory used for data transfers between the device and the driver,
// points to the memory inside TransferBuffer below
struct TransferDescriptor : fbl::DoublyLinkedListable<TransferDescriptor*> {
    uint8_t* virt;
    uintptr_t phys;
    uint32_t total_len;
    uint32_t used_len;
    uint32_t processed_len;
};

// Manages memory we use for transfers, TransferDescriptor points to the memory inside the class
class TransferBuffer {
public:
    TransferBuffer();
    ~TransferBuffer();

    zx_status_t Init(const zx::bti& bti, size_t count, uint32_t chunk_size);

    TransferDescriptor* GetDescriptor(size_t index);
    TransferDescriptor* PhysicalToDescriptor(uintptr_t phys);

private:
    size_t count_ = 0;
    size_t size_ = 0;
    uint32_t chunk_size_ = 0;

    io_buffer_t buf_;
    fbl::Array<TransferDescriptor> descriptor_;
};

// Just a list of descriptors
class TransferQueue {
public:
    void Add(TransferDescriptor* desc);
    TransferDescriptor* Peek();
    TransferDescriptor* Dequeue();
    bool IsEmpty() const;

private:
    fbl::DoublyLinkedList<TransferDescriptor*> queue_;
};

// Actual virtio console implementation
class ConsoleDevice : public Device {
public:
    explicit ConsoleDevice(zx_device_t* device, zx::bti bti, fbl::unique_ptr<Backend> backend);
    virtual ~ConsoleDevice();

    virtual zx_status_t Init() override;

    virtual void IrqRingUpdate() override;
    virtual void IrqConfigChange() override {}; // No need to handle configuration changes
    const char* tag() const override { return "virtio-console"; };

private:
    // For two queues it sums up to 32KiB, we probably don't need that much
    constexpr static size_t kDescriptors = 32;
    constexpr static uint32_t kChunkSize = 512;

    static zx_status_t virtio_console_read(void* ctx, void* buf, size_t len, zx_off_t off, size_t* actual);
    static zx_status_t virtio_console_write(void* ctx, const void* buf, size_t len, zx_off_t off, size_t* actual);

    zx_status_t Read(void* buf, size_t len, zx_off_t off, size_t* actual);
    zx_status_t Write(const void* buf, size_t len, zx_off_t off, size_t* actual);

    fbl::Mutex request_lock_;

    TransferBuffer port0_receive_buffer_ TA_GUARDED(request_lock_);
    TransferQueue port0_receive_descriptors_ TA_GUARDED(request_lock_);
    Ring port0_receive_queue_ TA_GUARDED(request_lock_) = {this};

    TransferBuffer port0_transmit_buffer_ TA_GUARDED(request_lock_);
    TransferQueue port0_transmit_descriptors_ TA_GUARDED(request_lock_);
    Ring port0_transmit_queue_ TA_GUARDED(request_lock_) = {this};
};

} // namespace virtio