/* vcc.c: sun4v virtual channel concentrator
 *
 * Copyright (C) 2017 Oracle. All rights reserved.
 */

#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/sysfs.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <asm/vio.h>
#include <asm/ldc.h>

#define DRV_MODULE_NAME         "vcc"
#define DRV_MODULE_VERSION      "1.1"
#define DRV_MODULE_RELDATE      "July 1, 2017"

static char version[] =
        DRV_MODULE_NAME ".c:v" DRV_MODULE_VERSION " (" DRV_MODULE_RELDATE ")";

MODULE_DESCRIPTION("Sun LDOM virtual console concentrator driver");
MODULE_LICENSE("GPL");
MODULE_VERSION(DRV_MODULE_VERSION);

struct vcc_port {
        struct vio_driver_state vio;

        spinlock_t lock;
        char *domain;
        struct tty_struct *tty; /* only populated while dev is open */
        unsigned long index;    /* index into the vcc_table */

        u64 refcnt;
        bool excl_locked;

        bool removed;

        /* This buffer is required to support the tty write_room interface
         * and guarantee that any characters that the driver accepts will
         * be eventually sent, either immediately or later.
         */
        int chars_in_buffer;
        struct vio_vcc buffer;

        struct timer_list rx_timer;
        struct timer_list tx_timer;
};

/* Microseconds that thread will delay waiting for a vcc port ref */
#define VCC_REF_DELAY           100

#define VCC_MAX_PORTS           1024
#define VCC_MINOR_START         0       /* must be zero */
#define VCC_BUFF_LEN            VIO_VCC_MTU_SIZE

#define VCC_CTL_BREAK           -1
#define VCC_CTL_HUP             -2

static const char vcc_driver_name[] = "vcc";
static const char vcc_device_node[] = "vcc";
static struct tty_driver *vcc_tty_driver;

static struct vcc_port *vcc_table[VCC_MAX_PORTS];
static DEFINE_SPINLOCK(vcc_table_lock);

int vcc_dbg;
int vcc_dbg_ldc;
int vcc_dbg_vio;

module_param(vcc_dbg, uint, 0664);
module_param(vcc_dbg_ldc, uint, 0664);
module_param(vcc_dbg_vio, uint, 0664);

#define VCC_DBG_DRV     0x1
#define VCC_DBG_LDC     0x2
#define VCC_DBG_PKT     0x4

#define vccdbg(f, a...)                                         \
        do {                                                    \
                if (vcc_dbg & VCC_DBG_DRV)                      \
                        pr_info(f, ## a);                       \
        } while (0)                                             \

#define vccdbgl(l)                                              \
        do {                                                    \
                if (vcc_dbg & VCC_DBG_LDC)                      \
                        ldc_print(l);                           \
        } while (0)                                             \

#define vccdbgp(pkt)                                            \
        do {                                                    \
                if (vcc_dbg & VCC_DBG_PKT) {                    \
                        int i;                                  \
                        for (i = 0; i < pkt.tag.stype; i++)     \
                                pr_info("[%c]", pkt.data[i]);   \
                }                                               \
        } while (0)                                             \

/* Note: Be careful when adding flags to this line discipline.  Don't
 * add anything that will cause echoing or we'll go into recursive
 * loop echoing chars back and forth with the console drivers.
 */
static const struct ktermios vcc_tty_termios = {
        .c_iflag = IGNBRK | IGNPAR,
        .c_oflag = OPOST,
        .c_cflag = B38400 | CS8 | CREAD | HUPCL,
        .c_cc = INIT_C_CC,
        .c_ispeed = 38400,
        .c_ospeed = 38400
};

/**
 * vcc_table_add() - Add VCC port to the VCC table
 * @port: pointer to the VCC port
 *
 * Return: index of the port in the VCC table on success,
 *         -1 on failure
 */
static int vcc_table_add(struct vcc_port *port)
{
        unsigned long flags;
        int i;

        spin_lock_irqsave(&vcc_table_lock, flags);
        for (i = VCC_MINOR_START; i < VCC_MAX_PORTS; i++) {
                if (!vcc_table[i]) {
                        vcc_table[i] = port;
                        break;
                }
        }
        spin_unlock_irqrestore(&vcc_table_lock, flags);

        if (i < VCC_MAX_PORTS)
                return i;
        else
                return -1;
}

/**
 * vcc_table_remove() - Removes a VCC port from the VCC table
 * @index: Index into the VCC table
 */
static void vcc_table_remove(unsigned long index)
{
        unsigned long flags;

        if (WARN_ON(index >= VCC_MAX_PORTS))
                return;

        spin_lock_irqsave(&vcc_table_lock, flags);
        vcc_table[index] = NULL;
        spin_unlock_irqrestore(&vcc_table_lock, flags);
}

/**
 * vcc_get() - Gets a reference to VCC port
 * @index: Index into the VCC table
 * @excl: Indicates if an exclusive access is requested
 *
 * Return: reference to the VCC port, if found
 *         NULL, if port not found
 */
static struct vcc_port *vcc_get(unsigned long index, bool excl)
{
        struct vcc_port *port;
        unsigned long flags;

try_again:
        spin_lock_irqsave(&vcc_table_lock, flags);

        port = vcc_table[index];
        if (!port) {
                spin_unlock_irqrestore(&vcc_table_lock, flags);
                return NULL;
        }

        if (!excl) {
                if (port->excl_locked) {
                        spin_unlock_irqrestore(&vcc_table_lock, flags);
                        udelay(VCC_REF_DELAY);
                        goto try_again;
                }
                port->refcnt++;
                spin_unlock_irqrestore(&vcc_table_lock, flags);
                return port;
        }

        if (port->refcnt) {
                spin_unlock_irqrestore(&vcc_table_lock, flags);
                /* Threads wanting exclusive access will wait half the time,
                 * probably giving them higher priority in the case of
                 * multiple waiters.
                 */
                udelay(VCC_REF_DELAY/2);
                goto try_again;
        }

        port->refcnt++;
        port->excl_locked = true;
        spin_unlock_irqrestore(&vcc_table_lock, flags);

        return port;
}

/**
 * vcc_put() - Returns a reference to VCC port
 * @port: pointer to VCC port
 * @excl: Indicates if the returned reference is an exclusive reference
 *
 * Note: It's the caller's responsibility to ensure the correct value
 *       for the excl flag
 */
static void vcc_put(struct vcc_port *port, bool excl)
{
        unsigned long flags;

        if (!port)
                return;

        spin_lock_irqsave(&vcc_table_lock, flags);

        /* check if caller attempted to put with the wrong flags */
        if (WARN_ON((excl && !port->excl_locked) ||
                    (!excl && port->excl_locked)))
                goto done;

        port->refcnt--;

        if (excl)
                port->excl_locked = false;

done:
        spin_unlock_irqrestore(&vcc_table_lock, flags);
}

/**
 * vcc_get_ne() - Get a non-exclusive reference to VCC port
 * @index: Index into the VCC table
 *
 * Gets a non-exclusive reference to VCC port, if it's not removed
 *
 * Return: pointer to the VCC port, if found
 *         NULL, if port not found
 */
static struct vcc_port *vcc_get_ne(unsigned long index)
{
        struct vcc_port *port;

        port = vcc_get(index, false);

        if (port && port->removed) {
                vcc_put(port, false);
                return NULL;
        }

        return port;
}

static void vcc_kick_rx(struct vcc_port *port)
{
        struct vio_driver_state *vio = &port->vio;

        assert_spin_locked(&port->lock);

        if (!timer_pending(&port->rx_timer) && !port->removed) {
                disable_irq_nosync(vio->vdev->rx_irq);
                port->rx_timer.expires = (jiffies + 1);
                add_timer(&port->rx_timer);
        }
}

static void vcc_kick_tx(struct vcc_port *port)
{
        assert_spin_locked(&port->lock);

        if (!timer_pending(&port->tx_timer) && !port->removed) {
                port->tx_timer.expires = (jiffies + 1);
                add_timer(&port->tx_timer);
        }
}

static int vcc_rx_check(struct tty_struct *tty, int size)
{
        if (WARN_ON(!tty || !tty->port))
                return 1;

        /* tty_buffer_request_room won't sleep because it uses
         * GFP_ATOMIC flag to allocate buffer
         */
        if (test_bit(TTY_THROTTLED, &tty->flags) ||
            (tty_buffer_request_room(tty->port, VCC_BUFF_LEN) < VCC_BUFF_LEN))
                return 0;

        return 1;
}

static int vcc_rx(struct tty_struct *tty, char *buf, int size)
{
        int len = 0;

        if (WARN_ON(!tty || !tty->port))
                return len;

        len = tty_insert_flip_string(tty->port, buf, size);
        if (len)
                tty_flip_buffer_push(tty->port);

        return len;
}

static int vcc_ldc_read(struct vcc_port *port)
{
        struct vio_driver_state *vio = &port->vio;
        struct tty_struct *tty;
        struct vio_vcc pkt;
        int rv = 0;

        tty = port->tty;
        if (!tty) {
                rv = ldc_rx_reset(vio->lp);
                vccdbg("VCC: reset rx q: rv=%d\n", rv);
                goto done;
        }

        /* Read as long as LDC has incoming data. */
        while (1) {
                if (!vcc_rx_check(tty, VIO_VCC_MTU_SIZE)) {
                        vcc_kick_rx(port);
                        break;
                }

                vccdbgl(vio->lp);

                rv = ldc_read(vio->lp, &pkt, sizeof(pkt));
                if (rv <= 0)
                        break;

                vccdbg("VCC: ldc_read()=%d\n", rv);
                vccdbg("TAG [%02x:%02x:%04x:%08x]\n",
                       pkt.tag.type, pkt.tag.stype,
                       pkt.tag.stype_env, pkt.tag.sid);

                if (pkt.tag.type == VIO_TYPE_DATA) {
                        vccdbgp(pkt);
                        /* vcc_rx_check ensures memory availability */
                        vcc_rx(tty, pkt.data, pkt.tag.stype);
                } else {
                        pr_err("VCC: unknown msg [%02x:%02x:%04x:%08x]\n",
                               pkt.tag.type, pkt.tag.stype,
                               pkt.tag.stype_env, pkt.tag.sid);
                        rv = -ECONNRESET;
                        break;
                }

                WARN_ON(rv != LDC_PACKET_SIZE);
        }

done:
        return rv;
}

static void vcc_rx_timer(struct timer_list *t)
{
        struct vcc_port *port = from_timer(port, t, rx_timer);
        struct vio_driver_state *vio;
        unsigned long flags;
        int rv;

        spin_lock_irqsave(&port->lock, flags);
        port->rx_timer.expires = 0;

        vio = &port->vio;

        enable_irq(vio->vdev->rx_irq);

        if (!port->tty || port->removed)
                goto done;

        rv = vcc_ldc_read(port);
        if (rv == -ECONNRESET)
                vio_conn_reset(vio);

done:
        spin_unlock_irqrestore(&port->lock, flags);
        vcc_put(port, false);
}

static void vcc_tx_timer(struct timer_list *t)
{
        struct vcc_port *port = from_timer(port, t, tx_timer);
        struct vio_vcc *pkt;
        unsigned long flags;
        int tosend = 0;
        int rv;

        spin_lock_irqsave(&port->lock, flags);
        port->tx_timer.expires = 0;

        if (!port->tty || port->removed)
                goto done;

        tosend = min(VCC_BUFF_LEN, port->chars_in_buffer);
        if (!tosend)
                goto done;

        pkt = &port->buffer;
        pkt->tag.type = VIO_TYPE_DATA;
        pkt->tag.stype = tosend;
        vccdbgl(port->vio.lp);

        rv = ldc_write(port->vio.lp, pkt, (VIO_TAG_SIZE + tosend));
        WARN_ON(!rv);

        if (rv < 0) {
                vccdbg("VCC: ldc_write()=%d\n", rv);
                vcc_kick_tx(port);
        } else {
                struct tty_struct *tty = port->tty;

                port->chars_in_buffer = 0;
                if (tty)
                        tty_wakeup(tty);
        }

done:
        spin_unlock_irqrestore(&port->lock, flags);
        vcc_put(port, false);
}

/**
 * vcc_event() - LDC event processing engine
 * @arg: VCC private data
 * @event: LDC event
 *
 * Handles LDC events for VCC
 */
static void vcc_event(void *arg, int event)
{
        struct vio_driver_state *vio;
        struct vcc_port *port;
        unsigned long flags;
        int rv;

        port = arg;
        vio = &port->vio;

        spin_lock_irqsave(&port->lock, flags);

        switch (event) {
        case LDC_EVENT_RESET:
        case LDC_EVENT_UP:
                vio_link_state_change(vio, event);
                break;

        case LDC_EVENT_DATA_READY:
                rv = vcc_ldc_read(port);
                if (rv == -ECONNRESET)
                        vio_conn_reset(vio);
                break;

        default:
                pr_err("VCC: unexpected LDC event(%d)\n", event);
        }

        spin_unlock_irqrestore(&port->lock, flags);
}

static struct ldc_channel_config vcc_ldc_cfg = {
        .event          = vcc_event,
        .mtu            = VIO_VCC_MTU_SIZE,
        .mode           = LDC_MODE_RAW,
        .debug          = 0,
};

/* Ordered from largest major to lowest */
static struct vio_version vcc_versions[] = {
        { .major = 1, .minor = 0 },
};

static struct tty_port_operations vcc_port_ops = { 0 };

static ssize_t vcc_sysfs_domain_show(struct device *dev,
                                     struct device_attribute *attr,
                                     char *buf)
{
        struct vcc_port *port;
        int rv;

        port = dev_get_drvdata(dev);
        if (!port)
                return -ENODEV;

        rv = scnprintf(buf, PAGE_SIZE, "%s\n", port->domain);

        return rv;
}

static int vcc_send_ctl(struct vcc_port *port, int ctl)
{
        struct vio_vcc pkt;
        int rv;

        pkt.tag.type = VIO_TYPE_CTRL;
        pkt.tag.sid = ctl;
        pkt.tag.stype = 0;

        rv = ldc_write(port->vio.lp, &pkt, sizeof(pkt.tag));
        WARN_ON(!rv);
        vccdbg("VCC: ldc_write(%ld)=%d\n", sizeof(pkt.tag), rv);

        return rv;
}

static ssize_t vcc_sysfs_break_store(struct device *dev,
                                     struct device_attribute *attr,
                                     const char *buf, size_t count)
{
        struct vcc_port *port;
        unsigned long flags;
        int rv = count;
        int brk;

        port = dev_get_drvdata(dev);
        if (!port)
                return -ENODEV;

        spin_lock_irqsave(&port->lock, flags);

        if (sscanf(buf, "%ud", &brk) != 1 || brk != 1)
                rv = -EINVAL;
        else if (vcc_send_ctl(port, VCC_CTL_BREAK) < 0)
                vcc_kick_tx(port);

        spin_unlock_irqrestore(&port->lock, flags);

        return rv;
}

static DEVICE_ATTR(domain, 0400, vcc_sysfs_domain_show, NULL);
static DEVICE_ATTR(break, 0200, NULL, vcc_sysfs_break_store);

static struct attribute *vcc_sysfs_entries[] = {
        &dev_attr_domain.attr,
        &dev_attr_break.attr,
        NULL
};

static struct attribute_group vcc_attribute_group = {
        .name = NULL,
        .attrs = vcc_sysfs_entries,
};

/**
 * vcc_probe() - Initialize VCC port
 * @vdev: Pointer to VIO device of the new VCC port
 * @id: VIO device ID
 *
 * Initializes a VCC port to receive serial console data from
 * the guest domain. Sets up a TTY end point on the control
 * domain. Sets up VIO/LDC link between the guest & control
 * domain endpoints.
 *
 * Return: status of the probe
 */
static int vcc_probe(struct vio_dev *vdev, const struct vio_device_id *id)
{
        struct mdesc_handle *hp;
        struct vcc_port *port;
        struct device *dev;
        const char *domain;
        char *name;
        u64 node;
        int rv;

        vccdbg("VCC: name=%s\n", dev_name(&vdev->dev));

        if (!vcc_tty_driver) {
                pr_err("VCC: TTY driver not registered\n");
                return -ENODEV;
        }

        port = kzalloc(sizeof(struct vcc_port), GFP_KERNEL);
        if (!port)
                return -ENOMEM;

        name = kstrdup(dev_name(&vdev->dev), GFP_KERNEL);

        rv = vio_driver_init(&port->vio, vdev, VDEV_CONSOLE_CON, vcc_versions,
                             ARRAY_SIZE(vcc_versions), NULL, name);
        if (rv)
                goto free_port;

        port->vio.debug = vcc_dbg_vio;
        vcc_ldc_cfg.debug = vcc_dbg_ldc;

        rv = vio_ldc_alloc(&port->vio, &vcc_ldc_cfg, port);
        if (rv)
                goto free_port;

        spin_lock_init(&port->lock);

        port->index = vcc_table_add(port);
        if (port->index == -1) {
                pr_err("VCC: no more TTY indices left for allocation\n");
                goto free_ldc;
        }

        /* Register the device using VCC table index as TTY index */
        dev = tty_register_device(vcc_tty_driver, port->index, &vdev->dev);
        if (IS_ERR(dev)) {
                rv = PTR_ERR(dev);
                goto free_table;
        }

        hp = mdesc_grab();

        node = vio_vdev_node(hp, vdev);
        if (node == MDESC_NODE_NULL) {
                rv = -ENXIO;
                mdesc_release(hp);
                goto unreg_tty;
        }

        domain = mdesc_get_property(hp, node, "vcc-domain-name", NULL);
        if (!domain) {
                rv = -ENXIO;
                mdesc_release(hp);
                goto unreg_tty;
        }
        port->domain = kstrdup(domain, GFP_KERNEL);

        mdesc_release(hp);

        rv = sysfs_create_group(&vdev->dev.kobj, &vcc_attribute_group);
        if (rv)
                goto free_domain;

        timer_setup(&port->rx_timer, vcc_rx_timer, 0);
        timer_setup(&port->tx_timer, vcc_tx_timer, 0);

        dev_set_drvdata(&vdev->dev, port);

        /* It's possible to receive IRQs in the middle of vio_port_up. Disable
         * IRQs until the port is up.
         */
        disable_irq_nosync(vdev->rx_irq);
        vio_port_up(&port->vio);
        enable_irq(vdev->rx_irq);

        return 0;

free_domain:
        kfree(port->domain);
unreg_tty:
        tty_unregister_device(vcc_tty_driver, port->index);
free_table:
        vcc_table_remove(port->index);
free_ldc:
        vio_ldc_free(&port->vio);
free_port:
        kfree(name);
        kfree(port);

        return rv;
}

/**
 * vcc_remove() - Terminate a VCC port
 * @vdev: Pointer to VIO device of the VCC port
 *
 * Terminates a VCC port. Sets up the teardown of TTY and
 * VIO/LDC link between guest and primary domains.
 *
 * Return: status of removal
 */
static int vcc_remove(struct vio_dev *vdev)
{
        struct vcc_port *port = dev_get_drvdata(&vdev->dev);

        if (!port)
                return -ENODEV;

        del_timer_sync(&port->rx_timer);
        del_timer_sync(&port->tx_timer);

        /* If there's a process with the device open, do a synchronous
         * hangup of the TTY. This *may* cause the process to call close
         * asynchronously, but it's not guaranteed.
         */
        if (port->tty)
                tty_vhangup(port->tty);

        /* Get exclusive reference to VCC, ensures that there are no other
         * clients to this port
         */
        port = vcc_get(port->index, true);

        if (WARN_ON(!port))
                return -ENODEV;

        tty_unregister_device(vcc_tty_driver, port->index);

        del_timer_sync(&port->vio.timer);
        vio_ldc_free(&port->vio);
        sysfs_remove_group(&vdev->dev.kobj, &vcc_attribute_group);
        dev_set_drvdata(&vdev->dev, NULL);
        if (port->tty) {
                port->removed = true;
                vcc_put(port, true);
        } else {
                vcc_table_remove(port->index);

                kfree(port->vio.name);
                kfree(port->domain);
                kfree(port);
        }

        return 0;
}

static const struct vio_device_id vcc_match[] = {
        {
                .type = "vcc-port",
        },
        {},
};
MODULE_DEVICE_TABLE(vio, vcc_match);

static struct vio_driver vcc_driver = {
        .id_table       = vcc_match,
        .probe          = vcc_probe,
        .remove         = vcc_remove,
        .name           = "vcc",
};

static int vcc_open(struct tty_struct *tty, struct file *vcc_file)
{
        struct vcc_port *port;

        if (unlikely(!tty)) {
                pr_err("VCC: open: Invalid TTY handle\n");
                return -ENXIO;
        }

        if (tty->count > 1)
                return -EBUSY;

        port = vcc_get_ne(tty->index);
        if (unlikely(!port)) {
                pr_err("VCC: open: Failed to find VCC port\n");
                return -ENODEV;
        }

        if (unlikely(!port->vio.lp)) {
                pr_err("VCC: open: LDC channel not configured\n");
                vcc_put(port, false);
                return -EPIPE;
        }
        vccdbgl(port->vio.lp);

        vcc_put(port, false);

        if (unlikely(!tty->port)) {
                pr_err("VCC: open: TTY port not found\n");
                return -ENXIO;
        }

        if (unlikely(!tty->port->ops)) {
                pr_err("VCC: open: TTY ops not defined\n");
                return -ENXIO;
        }

        return tty_port_open(tty->port, tty, vcc_file);
}

static void vcc_close(struct tty_struct *tty, struct file *vcc_file)
{
        if (unlikely(!tty)) {
                pr_err("VCC: close: Invalid TTY handle\n");
                return;
        }

        if (unlikely(tty->count > 1))
                return;

        if (unlikely(!tty->port)) {
                pr_err("VCC: close: TTY port not found\n");
                return;
        }

        tty_port_close(tty->port, tty, vcc_file);
}

static void vcc_ldc_hup(struct vcc_port *port)
{
        unsigned long flags;

        spin_lock_irqsave(&port->lock, flags);

        if (vcc_send_ctl(port, VCC_CTL_HUP) < 0)
                vcc_kick_tx(port);

        spin_unlock_irqrestore(&port->lock, flags);
}

static void vcc_hangup(struct tty_struct *tty)
{
        struct vcc_port *port;

        if (unlikely(!tty)) {
                pr_err("VCC: hangup: Invalid TTY handle\n");
                return;
        }

        port = vcc_get_ne(tty->index);
        if (unlikely(!port)) {
                pr_err("VCC: hangup: Failed to find VCC port\n");
                return;
        }

        if (unlikely(!tty->port)) {
                pr_err("VCC: hangup: TTY port not found\n");
                vcc_put(port, false);
                return;
        }

        vcc_ldc_hup(port);

        vcc_put(port, false);

        tty_port_hangup(tty->port);
}

static int vcc_write(struct tty_struct *tty, const unsigned char *buf,
                     int count)
{
        struct vcc_port *port;
        struct vio_vcc *pkt;
        unsigned long flags;
        int total_sent = 0;
        int tosend = 0;
        int rv = -EINVAL;

        if (unlikely(!tty)) {
                pr_err("VCC: write: Invalid TTY handle\n");
                return -ENXIO;
        }

        port = vcc_get_ne(tty->index);
        if (unlikely(!port)) {
                pr_err("VCC: write: Failed to find VCC port");
                return -ENODEV;
        }

        spin_lock_irqsave(&port->lock, flags);

        pkt = &port->buffer;
        pkt->tag.type = VIO_TYPE_DATA;

        while (count > 0) {
                /* Minimum of data to write and space available */
                tosend = min(count, (VCC_BUFF_LEN - port->chars_in_buffer));

                if (!tosend)
                        break;

                memcpy(&pkt->data[port->chars_in_buffer], &buf[total_sent],
                       tosend);
                port->chars_in_buffer += tosend;
                pkt->tag.stype = tosend;

                vccdbg("TAG [%02x:%02x:%04x:%08x]\n", pkt->tag.type,
                       pkt->tag.stype, pkt->tag.stype_env, pkt->tag.sid);
                vccdbg("DATA [%s]\n", pkt->data);
                vccdbgl(port->vio.lp);

                /* Since we know we have enough room in VCC buffer for tosend
                 * we record that it was sent regardless of whether the
                 * hypervisor actually took it because we have it buffered.
                 */
                rv = ldc_write(port->vio.lp, pkt, (VIO_TAG_SIZE + tosend));
                vccdbg("VCC: write: ldc_write(%d)=%d\n",
                       (VIO_TAG_SIZE + tosend), rv);

                total_sent += tosend;
                count -= tosend;
                if (rv < 0) {
                        vcc_kick_tx(port);
                        break;
                }

                port->chars_in_buffer = 0;
        }

        spin_unlock_irqrestore(&port->lock, flags);

        vcc_put(port, false);

        vccdbg("VCC: write: total=%d rv=%d", total_sent, rv);

        return total_sent ? total_sent : rv;
}

static int vcc_write_room(struct tty_struct *tty)
{
        struct vcc_port *port;
        u64 num;

        if (unlikely(!tty)) {
                pr_err("VCC: write_room: Invalid TTY handle\n");
                return -ENXIO;
        }

        port = vcc_get_ne(tty->index);
        if (unlikely(!port)) {
                pr_err("VCC: write_room: Failed to find VCC port\n");
                return 0;
        }

        num = VCC_BUFF_LEN - port->chars_in_buffer;

        vcc_put(port, false);

        return num;
}

static int vcc_chars_in_buffer(struct tty_struct *tty)
{
        struct vcc_port *port;
        u64 num;

        if (unlikely(!tty)) {
                pr_err("VCC: chars_in_buffer: Invalid TTY handle\n");
                return -ENXIO;
        }

        port = vcc_get_ne(tty->index);
        if (unlikely(!port)) {
                pr_err("VCC: chars_in_buffer: Failed to find VCC port\n");
                return -ENODEV;
        }

        num = port->chars_in_buffer;

        vcc_put(port, false);

        return num;
}

static int vcc_break_ctl(struct tty_struct *tty, int state)
{
        struct vcc_port *port;
        unsigned long flags;

        if (unlikely(!tty)) {
                pr_err("VCC: break_ctl: Invalid TTY handle\n");
                return -ENXIO;
        }

        port = vcc_get_ne(tty->index);
        if (unlikely(!port)) {
                pr_err("VCC: break_ctl: Failed to find VCC port\n");
                return -ENODEV;
        }

        /* Turn off break */
        if (state == 0) {
                vcc_put(port, false);
                return 0;
        }

        spin_lock_irqsave(&port->lock, flags);

        if (vcc_send_ctl(port, VCC_CTL_BREAK) < 0)
                vcc_kick_tx(port);

        spin_unlock_irqrestore(&port->lock, flags);

        vcc_put(port, false);

        return 0;
}

static int vcc_install(struct tty_driver *driver, struct tty_struct *tty)
{
        struct vcc_port *port_vcc;
        struct tty_port *port_tty;
        int ret;

        if (unlikely(!tty)) {
                pr_err("VCC: install: Invalid TTY handle\n");
                return -ENXIO;
        }

        if (tty->index >= VCC_MAX_PORTS)
                return -EINVAL;

        ret = tty_standard_install(driver, tty);

        if (ret)
                return ret;

        port_tty = kzalloc(sizeof(struct tty_port), GFP_KERNEL);
        if (!port_tty)
                return -ENOMEM;

        port_vcc = vcc_get(tty->index, true);
        if (!port_vcc) {
                pr_err("VCC: install: Failed to find VCC port\n");
                tty->port = NULL;
                kfree(port_tty);
                return -ENODEV;
        }

        tty_port_init(port_tty);
        port_tty->ops = &vcc_port_ops;
        tty->port = port_tty;

        port_vcc->tty = tty;

        vcc_put(port_vcc, true);

        return 0;
}

static void vcc_cleanup(struct tty_struct *tty)
{
        struct vcc_port *port;

        if (unlikely(!tty)) {
                pr_err("VCC: cleanup: Invalid TTY handle\n");
                return;
        }

        port = vcc_get(tty->index, true);
        if (port) {
                port->tty = NULL;

                if (port->removed) {
                        vcc_table_remove(tty->index);
                        kfree(port->vio.name);
                        kfree(port->domain);
                        kfree(port);
                } else {
                        vcc_put(port, true);
                }
        }

        tty_port_destroy(tty->port);
        kfree(tty->port);
        tty->port = NULL;
}

static const struct tty_operations vcc_ops = {
        .open                   = vcc_open,
        .close                  = vcc_close,
        .hangup                 = vcc_hangup,
        .write                  = vcc_write,
        .write_room             = vcc_write_room,
        .chars_in_buffer        = vcc_chars_in_buffer,
        .break_ctl              = vcc_break_ctl,
        .install                = vcc_install,
        .cleanup                = vcc_cleanup,
};

#define VCC_TTY_FLAGS   (TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_REAL_RAW)

static int vcc_tty_init(void)
{
        int rv;

        pr_info("VCC: %s\n", version);

        vcc_tty_driver = tty_alloc_driver(VCC_MAX_PORTS, VCC_TTY_FLAGS);
        if (IS_ERR(vcc_tty_driver)) {
                pr_err("VCC: TTY driver alloc failed\n");
                return PTR_ERR(vcc_tty_driver);
        }

        vcc_tty_driver->driver_name = vcc_driver_name;
        vcc_tty_driver->name = vcc_device_node;

        vcc_tty_driver->minor_start = VCC_MINOR_START;
        vcc_tty_driver->type = TTY_DRIVER_TYPE_SYSTEM;
        vcc_tty_driver->init_termios = vcc_tty_termios;

        tty_set_operations(vcc_tty_driver, &vcc_ops);

        rv = tty_register_driver(vcc_tty_driver);
        if (rv) {
                pr_err("VCC: TTY driver registration failed\n");
                put_tty_driver(vcc_tty_driver);
                vcc_tty_driver = NULL;
                return rv;
        }

        vccdbg("VCC: TTY driver registered\n");

        return 0;
}

static void vcc_tty_exit(void)
{
        tty_unregister_driver(vcc_tty_driver);
        put_tty_driver(vcc_tty_driver);
        vccdbg("VCC: TTY driver unregistered\n");

        vcc_tty_driver = NULL;
}

static int __init vcc_init(void)
{
        int rv;

        rv = vcc_tty_init();
        if (rv) {
                pr_err("VCC: TTY init failed\n");
                return rv;
        }

        rv = vio_register_driver(&vcc_driver);
        if (rv) {
                pr_err("VCC: VIO driver registration failed\n");
                vcc_tty_exit();
        } else {
                vccdbg("VCC: VIO driver registered successfully\n");
        }

        return rv;
}

static void __exit vcc_exit(void)
{
        vio_unregister_driver(&vcc_driver);
        vccdbg("VCC: VIO driver unregistered\n");
        vcc_tty_exit();
        vccdbg("VCC: TTY driver unregistered\n");
}

module_init(vcc_init);
module_exit(vcc_exit);