/******************************************************************************
 * Copyright (c) 2016 IBM Corporation
 * All rights reserved.
 * This program and the accompanying materials
 * are made available under the terms of the BSD License
 * which accompanies this distribution, and is available at
 * http://www.opensource.org/licenses/bsd-license.php
 *
 * Contributors:
 *     IBM Corporation - initial implementation
 *****************************************************************************/

/*
 * Virtio serial device definitions.
 * See Virtio 1.0 - 5.3 Console Device, for details
 */
#include <stdio.h>
#include <string.h>
#include <cpu.h>
#include <helpers.h>
#include <byteorder.h>
#include "virtio.h"
#include "virtio-serial.h"
#include "virtio-internal.h"

#define DRIVER_FEATURE_SUPPORT  VIRTIO_F_VERSION_1
#define RX_ELEM_SIZE            4
#define RX_NUM_ELEMS            128

#define RX_Q 0
#define TX_Q 1

static struct vqs vq_rx;
static struct vqs vq_tx;
static uint16_t last_rx_idx;	/* Last index in RX "used" ring */

int virtio_serial_init(struct virtio_device *dev)
{
	struct vring_avail *vq_avail;
	int status = VIRTIO_STAT_ACKNOWLEDGE;
	int i;

	/* Reset device */
	virtio_reset_device(dev);

	/* Acknowledge device. */
	virtio_set_status(dev, status);

	/* Tell HV that we know how to drive the device. */
	status |= VIRTIO_STAT_DRIVER;
	virtio_set_status(dev, status);

	if (dev->is_modern) {
		/* Negotiate features and sets FEATURES_OK if successful */
		if (virtio_negotiate_guest_features(dev, DRIVER_FEATURE_SUPPORT))
			goto dev_error;

		virtio_get_status(dev, &status);
	}

	if (virtio_queue_init_vq(dev, &vq_rx, RX_Q))
		goto dev_error;

	/* Allocate memory for multiple receive buffers */
	vq_rx.buf_mem = SLOF_alloc_mem(RX_ELEM_SIZE * RX_NUM_ELEMS);
	if (!vq_rx.buf_mem) {
		printf("virtio-serial: Failed to allocate buffers!\n");
		goto dev_error;
	}

	/* Prepare receive buffer queue */
	for (i = 0; i < RX_NUM_ELEMS; i++) {
		uint64_t addr = (uint64_t)vq_rx.buf_mem + i * RX_ELEM_SIZE;

		/* Descriptor for data: */
		virtio_fill_desc(&vq_rx.desc[i], dev->is_modern, addr, 1, VRING_DESC_F_WRITE, 0);
		vq_rx.avail->ring[i] = virtio_cpu_to_modern16(dev, i);
	}
	vq_rx.avail->flags = virtio_cpu_to_modern16(dev, VRING_AVAIL_F_NO_INTERRUPT);
	vq_rx.avail->idx = virtio_cpu_to_modern16(dev, RX_NUM_ELEMS);
	sync();

	last_rx_idx = virtio_modern16_to_cpu(dev, vq_rx.used->idx);

	if (virtio_queue_init_vq(dev, &vq_tx, TX_Q))
		goto dev_error;

	vq_avail = virtio_get_vring_avail(dev, TX_Q);
	vq_avail->flags = virtio_cpu_to_modern16(dev, VRING_AVAIL_F_NO_INTERRUPT);
	vq_avail->idx = 0;

	/* Tell HV that setup succeeded */
	status |= VIRTIO_STAT_DRIVER_OK;
	virtio_set_status(dev, status);

	return 1;
 dev_error:
	printf("%s: failed\n", __func__);
	status |= VIRTIO_STAT_FAILED;
	virtio_set_status(dev, status);
	return 0;
}

void virtio_serial_shutdown(struct virtio_device *dev)
{
	/* Quiesce device */
	virtio_set_status(dev, VIRTIO_STAT_FAILED);

	/* Reset device */
	virtio_reset_device(dev);
}

int virtio_serial_putchar(struct virtio_device *dev, char c)
{
	struct vring_desc *desc;
	int id;
	uint32_t vq_size, time;
	struct vring_desc *vq_desc;
	struct vring_avail *vq_avail;
	struct vring_used *vq_used;
	volatile uint16_t *current_used_idx;
	uint16_t last_used_idx, avail_idx;

	vq_size = virtio_get_qsize(dev, TX_Q);
	vq_desc = virtio_get_vring_desc(dev, TX_Q);
	vq_avail = virtio_get_vring_avail(dev, TX_Q);
	vq_used = virtio_get_vring_used(dev, TX_Q);

	avail_idx = virtio_modern16_to_cpu(dev, vq_avail->idx);

	last_used_idx = vq_used->idx;
	current_used_idx = &vq_used->idx;

	/* Determine descriptor index */
	id = avail_idx % vq_size;

	/* Set up virtqueue descriptor for header */
	desc = &vq_desc[id];
	virtio_fill_desc(desc, dev->is_modern, (uint64_t)&c, 1, 0, 0);

	vq_avail->ring[avail_idx % vq_size] = virtio_cpu_to_modern16 (dev, id);
	mb();
	vq_avail->idx = virtio_cpu_to_modern16(dev, avail_idx + 1);

	/* Tell HV that the queue is ready */
	virtio_queue_notify(dev, TX_Q);

	/* Wait for host to consume the descriptor */
	time = SLOF_GetTimer() + VIRTIO_TIMEOUT;
	while (*current_used_idx == last_used_idx) {
		// do something better
		mb();
		if (time < SLOF_GetTimer()) {
			printf("virtio_serial_putchar failed! \n");
			return 0;
		}
	}

	return 1;
}

static uint16_t last_rx_idx;	/* Last index in RX "used" ring */

char virtio_serial_getchar(struct virtio_device *dev)
{
	int id, idx;
	char buf[RX_NUM_ELEMS] = {0};
	uint16_t avail_idx;

	idx = virtio_modern16_to_cpu(dev, vq_rx.used->idx);
	if (last_rx_idx == idx) {
		/* Nothing received yet */
		return 0;
	}

	id = (virtio_modern32_to_cpu(dev, vq_rx.used->ring[last_rx_idx % vq_rx.size].id) + 1)
		% vq_rx.size;

	/* Copy data to destination buffer */
	memcpy(buf, (void *)virtio_modern64_to_cpu(dev, vq_rx.desc[id - 1].addr), RX_ELEM_SIZE);

	/* Move indices to next entries */
	last_rx_idx = last_rx_idx + 1;

	avail_idx = virtio_modern16_to_cpu(dev, vq_rx.avail->idx);
	vq_rx.avail->ring[avail_idx % vq_rx.size] = virtio_cpu_to_modern16(dev, id - 1);
	sync();
	vq_rx.avail->idx = virtio_cpu_to_modern16(dev, avail_idx + 1);
	sync();

	/* Tell HV that RX queue entry is ready */
	virtio_queue_notify(dev, RX_Q);

	return buf[0];
}

int virtio_serial_haschar(struct virtio_device *dev)
{
	if (last_rx_idx == virtio_modern16_to_cpu(dev, vq_rx.used->idx))
		return 0;
	else
		return 1;
}