// SPDX-License-Identifier: GPL-2.0+
/*
 * FireWire Serial driver
 *
 * Copyright (C) 2012 Peter Hurley <peter@hurleysoftware.com>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/device.h>
#include <linux/mod_devicetable.h>
#include <linux/rculist.h>
#include <linux/workqueue.h>
#include <linux/ratelimit.h>
#include <linux/bug.h>
#include <linux/uaccess.h>

#include "fwserial.h"

inline u64 be32_to_u64(__be32 hi, __be32 lo)
{
        return ((u64)be32_to_cpu(hi) << 32 | be32_to_cpu(lo));
}

#define LINUX_VENDOR_ID   0xd00d1eU  /* same id used in card root directory   */
#define FWSERIAL_VERSION  0x00e81cU  /* must be unique within LINUX_VENDOR_ID */

/* configurable options */
static int num_ttys = 4;            /* # of std ttys to create per fw_card    */
                                    /* - doubles as loopback port index       */
static bool auto_connect = true;    /* try to VIRT_CABLE to every peer        */
static bool create_loop_dev = true; /* create a loopback device for each card */

module_param_named(ttys, num_ttys, int, 0644);
module_param_named(auto, auto_connect, bool, 0644);
module_param_named(loop, create_loop_dev, bool, 0644);

/*
 * Threshold below which the tty is woken for writing
 * - should be equal to WAKEUP_CHARS in drivers/tty/n_tty.c because
 *   even if the writer is woken, n_tty_poll() won't set EPOLLOUT until
 *   our fifo is below this level
 */
#define WAKEUP_CHARS             256

/**
 * fwserial_list: list of every fw_serial created for each fw_card
 * See discussion in fwserial_probe.
 */
static LIST_HEAD(fwserial_list);
static DEFINE_MUTEX(fwserial_list_mutex);

/**
 * port_table: array of tty ports allocated to each fw_card
 *
 * tty ports are allocated during probe when an fw_serial is first
 * created for a given fw_card. Ports are allocated in a contiguous block,
 * each block consisting of 'num_ports' ports.
 */
static struct fwtty_port *port_table[MAX_TOTAL_PORTS];
static DEFINE_MUTEX(port_table_lock);
static bool port_table_corrupt;
#define FWTTY_INVALID_INDEX  MAX_TOTAL_PORTS

#define loop_idx(port)  (((port)->index) / num_ports)
#define table_idx(loop) ((loop) * num_ports + num_ttys)

/* total # of tty ports created per fw_card */
static int num_ports;

/* slab used as pool for struct fwtty_transactions */
static struct kmem_cache *fwtty_txn_cache;

struct tty_driver *fwtty_driver;
static struct tty_driver *fwloop_driver;

static struct dentry *fwserial_debugfs;

struct fwtty_transaction;
typedef void (*fwtty_transaction_cb)(struct fw_card *card, int rcode,
                                     void *data, size_t length,
                                     struct fwtty_transaction *txn);

struct fwtty_transaction {
        struct fw_transaction      fw_txn;
        fwtty_transaction_cb       callback;
        struct fwtty_port          *port;
        union {
                struct dma_pending dma_pended;
        };
};

#define to_device(a, b)                 (a->b)
#define fwtty_err(p, fmt, ...)                                          \
        dev_err(to_device(p, device), fmt, ##__VA_ARGS__)
#define fwtty_info(p, fmt, ...)                                         \
        dev_info(to_device(p, device), fmt, ##__VA_ARGS__)
#define fwtty_notice(p, fmt, ...)                                       \
        dev_notice(to_device(p, device), fmt, ##__VA_ARGS__)
#define fwtty_dbg(p, fmt, ...)                                          \
        dev_dbg(to_device(p, device), "%s: " fmt, __func__, ##__VA_ARGS__)
#define fwtty_err_ratelimited(p, fmt, ...)                              \
        dev_err_ratelimited(to_device(p, device), fmt, ##__VA_ARGS__)

#ifdef DEBUG
static inline void debug_short_write(struct fwtty_port *port, int c, int n)
{
        int avail;

        if (n < c) {
                spin_lock_bh(&port->lock);
                avail = dma_fifo_avail(&port->tx_fifo);
                spin_unlock_bh(&port->lock);
                fwtty_dbg(port, "short write: avail:%d req:%d wrote:%d\n",
                          avail, c, n);
        }
}
#else
#define debug_short_write(port, c, n)
#endif

static struct fwtty_peer *__fwserial_peer_by_node_id(struct fw_card *card,
                                                     int generation, int id);

#ifdef FWTTY_PROFILING

static void fwtty_profile_fifo(struct fwtty_port *port, unsigned int *stat)
{
        spin_lock_bh(&port->lock);
        fwtty_profile_data(stat, dma_fifo_avail(&port->tx_fifo));
        spin_unlock_bh(&port->lock);
}

static void fwtty_dump_profile(struct seq_file *m, struct stats *stats)
{
        /* for each stat, print sum of 0 to 2^k, then individually */
        int k = 4;
        unsigned int sum;
        int j;
        char t[10];

        snprintf(t, 10, "< %d", 1 << k);
        seq_printf(m, "\n%14s  %6s", " ", t);
        for (j = k + 1; j < DISTRIBUTION_MAX_INDEX; ++j)
                seq_printf(m, "%6d", 1 << j);

        ++k;
        for (j = 0, sum = 0; j <= k; ++j)
                sum += stats->reads[j];
        seq_printf(m, "\n%14s: %6d", "reads", sum);
        for (j = k + 1; j <= DISTRIBUTION_MAX_INDEX; ++j)
                seq_printf(m, "%6d", stats->reads[j]);

        for (j = 0, sum = 0; j <= k; ++j)
                sum += stats->writes[j];
        seq_printf(m, "\n%14s: %6d", "writes", sum);
        for (j = k + 1; j <= DISTRIBUTION_MAX_INDEX; ++j)
                seq_printf(m, "%6d", stats->writes[j]);

        for (j = 0, sum = 0; j <= k; ++j)
                sum += stats->txns[j];
        seq_printf(m, "\n%14s: %6d", "txns", sum);
        for (j = k + 1; j <= DISTRIBUTION_MAX_INDEX; ++j)
                seq_printf(m, "%6d", stats->txns[j]);

        for (j = 0, sum = 0; j <= k; ++j)
                sum += stats->unthrottle[j];
        seq_printf(m, "\n%14s: %6d", "avail @ unthr", sum);
        for (j = k + 1; j <= DISTRIBUTION_MAX_INDEX; ++j)
                seq_printf(m, "%6d", stats->unthrottle[j]);
}

#else
#define fwtty_profile_fifo(port, stat)
#define fwtty_dump_profile(m, stats)
#endif

/*
 * Returns the max receive packet size for the given node
 * Devices which are OHCI v1.0/ v1.1/ v1.2-draft or RFC 2734 compliant
 * are required by specification to support max_rec of 8 (512 bytes) or more.
 */
static inline int device_max_receive(struct fw_device *fw_device)
{
        /* see IEEE 1394-2008 table 8-8 */
        return min(2 << fw_device->max_rec, 4096);
}

static void fwtty_log_tx_error(struct fwtty_port *port, int rcode)
{
        switch (rcode) {
        case RCODE_SEND_ERROR:
                fwtty_err_ratelimited(port, "card busy\n");
                break;
        case RCODE_ADDRESS_ERROR:
                fwtty_err_ratelimited(port, "bad unit addr or write length\n");
                break;
        case RCODE_DATA_ERROR:
                fwtty_err_ratelimited(port, "failed rx\n");
                break;
        case RCODE_NO_ACK:
                fwtty_err_ratelimited(port, "missing ack\n");
                break;
        case RCODE_BUSY:
                fwtty_err_ratelimited(port, "remote busy\n");
                break;
        default:
                fwtty_err_ratelimited(port, "failed tx: %d\n", rcode);
        }
}

static void fwtty_common_callback(struct fw_card *card, int rcode,
                                  void *payload, size_t len, void *cb_data)
{
        struct fwtty_transaction *txn = cb_data;
        struct fwtty_port *port = txn->port;

        if (port && rcode != RCODE_COMPLETE)
                fwtty_log_tx_error(port, rcode);
        if (txn->callback)
                txn->callback(card, rcode, payload, len, txn);
        kmem_cache_free(fwtty_txn_cache, txn);
}

static int fwtty_send_data_async(struct fwtty_peer *peer, int tcode,
                                 unsigned long long addr, void *payload,
                                 size_t len, fwtty_transaction_cb callback,
                                 struct fwtty_port *port)
{
        struct fwtty_transaction *txn;
        int generation;

        txn = kmem_cache_alloc(fwtty_txn_cache, GFP_ATOMIC);
        if (!txn)
                return -ENOMEM;

        txn->callback = callback;
        txn->port = port;

        generation = peer->generation;
        smp_rmb();
        fw_send_request(peer->serial->card, &txn->fw_txn, tcode,
                        peer->node_id, generation, peer->speed, addr, payload,
                        len, fwtty_common_callback, txn);
        return 0;
}

static void fwtty_send_txn_async(struct fwtty_peer *peer,
                                 struct fwtty_transaction *txn, int tcode,
                                 unsigned long long addr, void *payload,
                                 size_t len, fwtty_transaction_cb callback,
                                 struct fwtty_port *port)
{
        int generation;

        txn->callback = callback;
        txn->port = port;

        generation = peer->generation;
        smp_rmb();
        fw_send_request(peer->serial->card, &txn->fw_txn, tcode,
                        peer->node_id, generation, peer->speed, addr, payload,
                        len, fwtty_common_callback, txn);
}

static void __fwtty_restart_tx(struct fwtty_port *port)
{
        int len, avail;

        len = dma_fifo_out_level(&port->tx_fifo);
        if (len)
                schedule_delayed_work(&port->drain, 0);
        avail = dma_fifo_avail(&port->tx_fifo);

        fwtty_dbg(port, "fifo len: %d avail: %d\n", len, avail);
}

static void fwtty_restart_tx(struct fwtty_port *port)
{
        spin_lock_bh(&port->lock);
        __fwtty_restart_tx(port);
        spin_unlock_bh(&port->lock);
}

/**
 * fwtty_update_port_status - decodes & dispatches line status changes
 *
 * Note: in loopback, the port->lock is being held. Only use functions that
 * don't attempt to reclaim the port->lock.
 */
static void fwtty_update_port_status(struct fwtty_port *port,
                                     unsigned int status)
{
        unsigned int delta;
        struct tty_struct *tty;

        /* simulated LSR/MSR status from remote */
        status &= ~MCTRL_MASK;
        delta = (port->mstatus ^ status) & ~MCTRL_MASK;
        delta &= ~(status & TIOCM_RNG);
        port->mstatus = status;

        if (delta & TIOCM_RNG)
                ++port->icount.rng;
        if (delta & TIOCM_DSR)
                ++port->icount.dsr;
        if (delta & TIOCM_CAR)
                ++port->icount.dcd;
        if (delta & TIOCM_CTS)
                ++port->icount.cts;

        fwtty_dbg(port, "status: %x delta: %x\n", status, delta);

        if (delta & TIOCM_CAR) {
                tty = tty_port_tty_get(&port->port);
                if (tty && !C_CLOCAL(tty)) {
                        if (status & TIOCM_CAR)
                                wake_up_interruptible(&port->port.open_wait);
                        else
                                schedule_work(&port->hangup);
                }
                tty_kref_put(tty);
        }

        if (delta & TIOCM_CTS) {
                tty = tty_port_tty_get(&port->port);
                if (tty && C_CRTSCTS(tty)) {
                        if (tty->hw_stopped) {
                                if (status & TIOCM_CTS) {
                                        tty->hw_stopped = 0;
                                        if (port->loopback)
                                                __fwtty_restart_tx(port);
                                        else
                                                fwtty_restart_tx(port);
                                }
                        } else {
                                if (~status & TIOCM_CTS)
                                        tty->hw_stopped = 1;
                        }
                }
                tty_kref_put(tty);

        } else if (delta & OOB_TX_THROTTLE) {
                tty = tty_port_tty_get(&port->port);
                if (tty) {
                        if (tty->hw_stopped) {
                                if (~status & OOB_TX_THROTTLE) {
                                        tty->hw_stopped = 0;
                                        if (port->loopback)
                                                __fwtty_restart_tx(port);
                                        else
                                                fwtty_restart_tx(port);
                                }
                        } else {
                                if (status & OOB_TX_THROTTLE)
                                        tty->hw_stopped = 1;
                        }
                }
                tty_kref_put(tty);
        }

        if (delta & (UART_LSR_BI << 24)) {
                if (status & (UART_LSR_BI << 24)) {
                        port->break_last = jiffies;
                        schedule_delayed_work(&port->emit_breaks, 0);
                } else {
                        /* run emit_breaks one last time (if pending) */
                        mod_delayed_work(system_wq, &port->emit_breaks, 0);
                }
        }

        if (delta & (TIOCM_DSR | TIOCM_CAR | TIOCM_CTS | TIOCM_RNG))
                wake_up_interruptible(&port->port.delta_msr_wait);
}

/**
 * __fwtty_port_line_status - generate 'line status' for indicated port
 *
 * This function returns a remote 'MSR' state based on the local 'MCR' state,
 * as if a null modem cable was attached. The actual status is a mangling
 * of TIOCM_* bits suitable for sending to a peer's status_addr.
 *
 * Note: caller must be holding port lock
 */
static unsigned int __fwtty_port_line_status(struct fwtty_port *port)
{
        unsigned int status = 0;

        /* TODO: add module param to tie RNG to DTR as well */

        if (port->mctrl & TIOCM_DTR)
                status |= TIOCM_DSR | TIOCM_CAR;
        if (port->mctrl & TIOCM_RTS)
                status |= TIOCM_CTS;
        if (port->mctrl & OOB_RX_THROTTLE)
                status |= OOB_TX_THROTTLE;
        /* emulate BRK as add'l line status */
        if (port->break_ctl)
                status |= UART_LSR_BI << 24;

        return status;
}

/**
 * __fwtty_write_port_status - send the port line status to peer
 *
 * Note: caller must be holding the port lock.
 */
static int __fwtty_write_port_status(struct fwtty_port *port)
{
        struct fwtty_peer *peer;
        int err = -ENOENT;
        unsigned int status = __fwtty_port_line_status(port);

        rcu_read_lock();
        peer = rcu_dereference(port->peer);
        if (peer) {
                err = fwtty_send_data_async(peer, TCODE_WRITE_QUADLET_REQUEST,
                                            peer->status_addr, &status,
                                            sizeof(status), NULL, port);
        }
        rcu_read_unlock();

        return err;
}

/**
 * fwtty_write_port_status - same as above but locked by port lock
 */
static int fwtty_write_port_status(struct fwtty_port *port)
{
        int err;

        spin_lock_bh(&port->lock);
        err = __fwtty_write_port_status(port);
        spin_unlock_bh(&port->lock);
        return err;
}

static void fwtty_throttle_port(struct fwtty_port *port)
{
        struct tty_struct *tty;
        unsigned int old;

        tty = tty_port_tty_get(&port->port);
        if (!tty)
                return;

        spin_lock_bh(&port->lock);

        old = port->mctrl;
        port->mctrl |= OOB_RX_THROTTLE;
        if (C_CRTSCTS(tty))
                port->mctrl &= ~TIOCM_RTS;
        if (~old & OOB_RX_THROTTLE)
                __fwtty_write_port_status(port);

        spin_unlock_bh(&port->lock);

        tty_kref_put(tty);
}

/**
 * fwtty_do_hangup - wait for ldisc to deliver all pending rx; only then hangup
 *
 * When the remote has finished tx, and all in-flight rx has been received and
 * and pushed to the flip buffer, the remote may close its device. This will
 * drop DTR on the remote which will drop carrier here. Typically, the tty is
 * hung up when carrier is dropped or lost.
 *
 * However, there is a race between the hang up and the line discipline
 * delivering its data to the reader. A hangup will cause the ldisc to flush
 * (ie., clear) the read buffer and flip buffer. Because of firewire's
 * relatively high throughput, the ldisc frequently lags well behind the driver,
 * resulting in lost data (which has already been received and written to
 * the flip buffer) when the remote closes its end.
 *
 * Unfortunately, since the flip buffer offers no direct method for determining
 * if it holds data, ensuring the ldisc has delivered all data is problematic.
 */

/* FIXME: drop this workaround when __tty_hangup waits for ldisc completion */
static void fwtty_do_hangup(struct work_struct *work)
{
        struct fwtty_port *port = to_port(work, hangup);
        struct tty_struct *tty;

        schedule_timeout_uninterruptible(msecs_to_jiffies(50));

        tty = tty_port_tty_get(&port->port);
        if (tty)
                tty_vhangup(tty);
        tty_kref_put(tty);
}

static void fwtty_emit_breaks(struct work_struct *work)
{
        struct fwtty_port *port = to_port(to_delayed_work(work), emit_breaks);
        static const char buf[16];
        unsigned long now = jiffies;
        unsigned long elapsed = now - port->break_last;
        int n, t, c, brk = 0;

        /* generate breaks at the line rate (but at least 1) */
        n = (elapsed * port->cps) / HZ + 1;
        port->break_last = now;

        fwtty_dbg(port, "sending %d brks\n", n);

        while (n) {
                t = min(n, 16);
                c = tty_insert_flip_string_fixed_flag(&port->port, buf,
                                                      TTY_BREAK, t);
                n -= c;
                brk += c;
                if (c < t)
                        break;
        }
        tty_flip_buffer_push(&port->port);

        if (port->mstatus & (UART_LSR_BI << 24))
                schedule_delayed_work(&port->emit_breaks, FREQ_BREAKS);
        port->icount.brk += brk;
}

static int fwtty_rx(struct fwtty_port *port, unsigned char *data, size_t len)
{
        int c, n = len;
        unsigned int lsr;
        int err = 0;

        fwtty_dbg(port, "%d\n", n);
        fwtty_profile_data(port->stats.reads, n);

        if (port->write_only) {
                n = 0;
                goto out;
        }

        /* disregard break status; breaks are generated by emit_breaks work */
        lsr = (port->mstatus >> 24) & ~UART_LSR_BI;

        if (port->overrun)
                lsr |= UART_LSR_OE;

        if (lsr & UART_LSR_OE)
                ++port->icount.overrun;

        lsr &= port->status_mask;
        if (lsr & ~port->ignore_mask & UART_LSR_OE) {
                if (!tty_insert_flip_char(&port->port, 0, TTY_OVERRUN)) {
                        err = -EIO;
                        goto out;
                }
        }
        port->overrun = false;

        if (lsr & port->ignore_mask & ~UART_LSR_OE) {
                /* TODO: don't drop SAK and Magic SysRq here */
                n = 0;
                goto out;
        }

        c = tty_insert_flip_string_fixed_flag(&port->port, data, TTY_NORMAL, n);
        if (c > 0)
                tty_flip_buffer_push(&port->port);
        n -= c;

        if (n) {
                port->overrun = true;
                err = -EIO;
                fwtty_err_ratelimited(port, "flip buffer overrun\n");

        } else {
                /* throttle the sender if remaining flip buffer space has
                 * reached high watermark to avoid losing data which may be
                 * in-flight. Since the AR request context is 32k, that much
                 * data may have _already_ been acked.
                 */
                if (tty_buffer_space_avail(&port->port) < HIGH_WATERMARK)
                        fwtty_throttle_port(port);
        }

out:
        port->icount.rx += len;
        port->stats.lost += n;
        return err;
}

/**
 * fwtty_port_handler - bus address handler for port reads/writes
 * @parameters: fw_address_callback_t as specified by firewire core interface
 *
 * This handler is responsible for handling inbound read/write dma from remotes.
 */
static void fwtty_port_handler(struct fw_card *card,
                               struct fw_request *request,
                               int tcode, int destination, int source,
                               int generation,
                               unsigned long long addr,
                               void *data, size_t len,
                               void *callback_data)
{
        struct fwtty_port *port = callback_data;
        struct fwtty_peer *peer;
        int err;
        int rcode;

        /* Only accept rx from the peer virtual-cabled to this port */
        rcu_read_lock();
        peer = __fwserial_peer_by_node_id(card, generation, source);
        rcu_read_unlock();
        if (!peer || peer != rcu_access_pointer(port->peer)) {
                rcode = RCODE_ADDRESS_ERROR;
                fwtty_err_ratelimited(port, "ignoring unauthenticated data\n");
                goto respond;
        }

        switch (tcode) {
        case TCODE_WRITE_QUADLET_REQUEST:
                if (addr != port->rx_handler.offset || len != 4) {
                        rcode = RCODE_ADDRESS_ERROR;
                } else {
                        fwtty_update_port_status(port, *(unsigned int *)data);
                        rcode = RCODE_COMPLETE;
                }
                break;

        case TCODE_WRITE_BLOCK_REQUEST:
                if (addr != port->rx_handler.offset + 4 ||
                    len > port->rx_handler.length - 4) {
                        rcode = RCODE_ADDRESS_ERROR;
                } else {
                        err = fwtty_rx(port, data, len);
                        switch (err) {
                        case 0:
                                rcode = RCODE_COMPLETE;
                                break;
                        case -EIO:
                                rcode = RCODE_DATA_ERROR;
                                break;
                        default:
                                rcode = RCODE_CONFLICT_ERROR;
                                break;
                        }
                }
                break;

        default:
                rcode = RCODE_TYPE_ERROR;
        }

respond:
        fw_send_response(card, request, rcode);
}

/**
 * fwtty_tx_complete - callback for tx dma
 * @data: ignored, has no meaning for write txns
 * @length: ignored, has no meaning for write txns
 *
 * The writer must be woken here if the fifo has been emptied because it
 * may have slept if chars_in_buffer was != 0
 */
static void fwtty_tx_complete(struct fw_card *card, int rcode,
                              void *data, size_t length,
                              struct fwtty_transaction *txn)
{
        struct fwtty_port *port = txn->port;
        int len;

        fwtty_dbg(port, "rcode: %d\n", rcode);

        switch (rcode) {
        case RCODE_COMPLETE:
                spin_lock_bh(&port->lock);
                dma_fifo_out_complete(&port->tx_fifo, &txn->dma_pended);
                len = dma_fifo_level(&port->tx_fifo);
                spin_unlock_bh(&port->lock);

                port->icount.tx += txn->dma_pended.len;
                break;

        default:
                /* TODO: implement retries */
                spin_lock_bh(&port->lock);
                dma_fifo_out_complete(&port->tx_fifo, &txn->dma_pended);
                len = dma_fifo_level(&port->tx_fifo);
                spin_unlock_bh(&port->lock);

                port->stats.dropped += txn->dma_pended.len;
        }

        if (len < WAKEUP_CHARS)
                tty_port_tty_wakeup(&port->port);
}

static int fwtty_tx(struct fwtty_port *port, bool drain)
{
        struct fwtty_peer *peer;
        struct fwtty_transaction *txn;
        struct tty_struct *tty;
        int n, len;

        tty = tty_port_tty_get(&port->port);
        if (!tty)
                return -ENOENT;

        rcu_read_lock();
        peer = rcu_dereference(port->peer);
        if (!peer) {
                n = -EIO;
                goto out;
        }

        if (test_and_set_bit(IN_TX, &port->flags)) {
                n = -EALREADY;
                goto out;
        }

        /* try to write as many dma transactions out as possible */
        n = -EAGAIN;
        while (!tty->stopped && !tty->hw_stopped &&
               !test_bit(STOP_TX, &port->flags)) {
                txn = kmem_cache_alloc(fwtty_txn_cache, GFP_ATOMIC);
                if (!txn) {
                        n = -ENOMEM;
                        break;
                }

                spin_lock_bh(&port->lock);
                n = dma_fifo_out_pend(&port->tx_fifo, &txn->dma_pended);
                spin_unlock_bh(&port->lock);

                fwtty_dbg(port, "out: %u rem: %d\n", txn->dma_pended.len, n);

                if (n < 0) {
                        kmem_cache_free(fwtty_txn_cache, txn);
                        if (n == -EAGAIN) {
                                ++port->stats.tx_stall;
                        } else if (n == -ENODATA) {
                                fwtty_profile_data(port->stats.txns, 0);
                        } else {
                                ++port->stats.fifo_errs;
                                fwtty_err_ratelimited(port, "fifo err: %d\n",
                                                      n);
                        }
                        break;
                }

                fwtty_profile_data(port->stats.txns, txn->dma_pended.len);

                fwtty_send_txn_async(peer, txn, TCODE_WRITE_BLOCK_REQUEST,
                                     peer->fifo_addr, txn->dma_pended.data,
                                     txn->dma_pended.len, fwtty_tx_complete,
                                     port);
                ++port->stats.sent;

                /*
                 * Stop tx if the 'last view' of the fifo is empty or if
                 * this is the writer and there's not enough data to bother
                 */
                if (n == 0 || (!drain && n < WRITER_MINIMUM))
                        break;
        }

        if (n >= 0 || n == -EAGAIN || n == -ENOMEM || n == -ENODATA) {
                spin_lock_bh(&port->lock);
                len = dma_fifo_out_level(&port->tx_fifo);
                if (len) {
                        unsigned long delay = (n == -ENOMEM) ? HZ : 1;

                        schedule_delayed_work(&port->drain, delay);
                }
                len = dma_fifo_level(&port->tx_fifo);
                spin_unlock_bh(&port->lock);

                /* wakeup the writer */
                if (drain && len < WAKEUP_CHARS)
                        tty_wakeup(tty);
        }

        clear_bit(IN_TX, &port->flags);
        wake_up_interruptible(&port->wait_tx);

out:
        rcu_read_unlock();
        tty_kref_put(tty);
        return n;
}

static void fwtty_drain_tx(struct work_struct *work)
{
        struct fwtty_port *port = to_port(to_delayed_work(work), drain);

        fwtty_tx(port, true);
}

static void fwtty_write_xchar(struct fwtty_port *port, char ch)
{
        struct fwtty_peer *peer;

        ++port->stats.xchars;

        fwtty_dbg(port, "%02x\n", ch);

        rcu_read_lock();
        peer = rcu_dereference(port->peer);
        if (peer) {
                fwtty_send_data_async(peer, TCODE_WRITE_BLOCK_REQUEST,
                                      peer->fifo_addr, &ch, sizeof(ch),
                                      NULL, port);
        }
        rcu_read_unlock();
}

static struct fwtty_port *fwtty_port_get(unsigned int index)
{
        struct fwtty_port *port;

        if (index >= MAX_TOTAL_PORTS)
                return NULL;

        mutex_lock(&port_table_lock);
        port = port_table[index];
        if (port)
                kref_get(&port->serial->kref);
        mutex_unlock(&port_table_lock);
        return port;
}

static int fwtty_ports_add(struct fw_serial *serial)
{
        int err = -EBUSY;
        int i, j;

        if (port_table_corrupt)
                return err;

        mutex_lock(&port_table_lock);
        for (i = 0; i + num_ports <= MAX_TOTAL_PORTS; i += num_ports) {
                if (!port_table[i]) {
                        for (j = 0; j < num_ports; ++i, ++j) {
                                serial->ports[j]->index = i;
                                port_table[i] = serial->ports[j];
                        }
                        err = 0;
                        break;
                }
        }
        mutex_unlock(&port_table_lock);
        return err;
}

static void fwserial_destroy(struct kref *kref)
{
        struct fw_serial *serial = to_serial(kref, kref);
        struct fwtty_port **ports = serial->ports;
        int j, i = ports[0]->index;

        synchronize_rcu();

        mutex_lock(&port_table_lock);
        for (j = 0; j < num_ports; ++i, ++j) {
                port_table_corrupt |= port_table[i] != ports[j];
                WARN_ONCE(port_table_corrupt, "port_table[%d]: %p != ports[%d]: %p",
                          i, port_table[i], j, ports[j]);

                port_table[i] = NULL;
        }
        mutex_unlock(&port_table_lock);

        for (j = 0; j < num_ports; ++j) {
                fw_core_remove_address_handler(&ports[j]->rx_handler);
                tty_port_destroy(&ports[j]->port);
                kfree(ports[j]);
        }
        kfree(serial);
}

static void fwtty_port_put(struct fwtty_port *port)
{
        kref_put(&port->serial->kref, fwserial_destroy);
}

static void fwtty_port_dtr_rts(struct tty_port *tty_port, int on)
{
        struct fwtty_port *port = to_port(tty_port, port);

        fwtty_dbg(port, "on/off: %d\n", on);

        spin_lock_bh(&port->lock);
        /* Don't change carrier state if this is a console */
        if (!port->port.console) {
                if (on)
                        port->mctrl |= TIOCM_DTR | TIOCM_RTS;
                else
                        port->mctrl &= ~(TIOCM_DTR | TIOCM_RTS);
        }

        __fwtty_write_port_status(port);
        spin_unlock_bh(&port->lock);
}

/**
 * fwtty_port_carrier_raised: required tty_port operation
 *
 * This port operation is polled after a tty has been opened and is waiting for
 * carrier detect -- see drivers/tty/tty_port:tty_port_block_til_ready().
 */
static int fwtty_port_carrier_raised(struct tty_port *tty_port)
{
        struct fwtty_port *port = to_port(tty_port, port);
        int rc;

        rc = (port->mstatus & TIOCM_CAR);

        fwtty_dbg(port, "%d\n", rc);

        return rc;
}

static unsigned int set_termios(struct fwtty_port *port, struct tty_struct *tty)
{
        unsigned int baud, frame;

        baud = tty_termios_baud_rate(&tty->termios);
        tty_termios_encode_baud_rate(&tty->termios, baud, baud);

        /* compute bit count of 2 frames */
        frame = 12 + ((C_CSTOPB(tty)) ? 4 : 2) + ((C_PARENB(tty)) ? 2 : 0);

        switch (C_CSIZE(tty)) {
        case CS5:
                frame -= (C_CSTOPB(tty)) ? 1 : 0;
                break;
        case CS6:
                frame += 2;
                break;
        case CS7:
                frame += 4;
                break;
        case CS8:
                frame += 6;
                break;
        }

        port->cps = (baud << 1) / frame;

        port->status_mask = UART_LSR_OE;
        if (_I_FLAG(tty, BRKINT | PARMRK))
                port->status_mask |= UART_LSR_BI;

        port->ignore_mask = 0;
        if (I_IGNBRK(tty)) {
                port->ignore_mask |= UART_LSR_BI;
                if (I_IGNPAR(tty))
                        port->ignore_mask |= UART_LSR_OE;
        }

        port->write_only = !C_CREAD(tty);

        /* turn off echo and newline xlat if loopback */
        if (port->loopback) {
                tty->termios.c_lflag &= ~(ECHO | ECHOE | ECHOK | ECHOKE |
                                          ECHONL | ECHOPRT | ECHOCTL);
                tty->termios.c_oflag &= ~ONLCR;
        }

        return baud;
}

static int fwtty_port_activate(struct tty_port *tty_port,
                               struct tty_struct *tty)
{
        struct fwtty_port *port = to_port(tty_port, port);
        unsigned int baud;
        int err;

        set_bit(TTY_IO_ERROR, &tty->flags);

        err = dma_fifo_alloc(&port->tx_fifo, FWTTY_PORT_TXFIFO_LEN,
                             cache_line_size(),
                             port->max_payload,
                             FWTTY_PORT_MAX_PEND_DMA,
                             GFP_KERNEL);
        if (err)
                return err;

        spin_lock_bh(&port->lock);

        baud = set_termios(port, tty);

        /* if console, don't change carrier state */
        if (!port->port.console) {
                port->mctrl = 0;
                if (baud != 0)
                        port->mctrl = TIOCM_DTR | TIOCM_RTS;

        }

        if (C_CRTSCTS(tty) && ~port->mstatus & TIOCM_CTS)
                tty->hw_stopped = 1;

        __fwtty_write_port_status(port);
        spin_unlock_bh(&port->lock);

        clear_bit(TTY_IO_ERROR, &tty->flags);

        return 0;
}

/**
 * fwtty_port_shutdown
 *
 * Note: the tty port core ensures this is not the console and
 * manages TTY_IO_ERROR properly
 */
static void fwtty_port_shutdown(struct tty_port *tty_port)
{
        struct fwtty_port *port = to_port(tty_port, port);

        /* TODO: cancel outstanding transactions */

        cancel_delayed_work_sync(&port->emit_breaks);
        cancel_delayed_work_sync(&port->drain);

        spin_lock_bh(&port->lock);
        port->flags = 0;
        port->break_ctl = 0;
        port->overrun = 0;
        __fwtty_write_port_status(port);
        dma_fifo_free(&port->tx_fifo);
        spin_unlock_bh(&port->lock);
}

static int fwtty_open(struct tty_struct *tty, struct file *fp)
{
        struct fwtty_port *port = tty->driver_data;

        return tty_port_open(&port->port, tty, fp);
}

static void fwtty_close(struct tty_struct *tty, struct file *fp)
{
        struct fwtty_port *port = tty->driver_data;

        tty_port_close(&port->port, tty, fp);
}

static void fwtty_hangup(struct tty_struct *tty)
{
        struct fwtty_port *port = tty->driver_data;

        tty_port_hangup(&port->port);
}

static void fwtty_cleanup(struct tty_struct *tty)
{
        struct fwtty_port *port = tty->driver_data;

        tty->driver_data = NULL;
        fwtty_port_put(port);
}

static int fwtty_install(struct tty_driver *driver, struct tty_struct *tty)
{
        struct fwtty_port *port = fwtty_port_get(tty->index);
        int err;

        err = tty_standard_install(driver, tty);
        if (!err)
                tty->driver_data = port;
        else
                fwtty_port_put(port);
        return err;
}

static int fwloop_install(struct tty_driver *driver, struct tty_struct *tty)
{
        struct fwtty_port *port = fwtty_port_get(table_idx(tty->index));
        int err;

        err = tty_standard_install(driver, tty);
        if (!err)
                tty->driver_data = port;
        else
                fwtty_port_put(port);
        return err;
}

static int fwtty_write(struct tty_struct *tty, const unsigned char *buf, int c)
{
        struct fwtty_port *port = tty->driver_data;
        int n, len;

        fwtty_dbg(port, "%d\n", c);
        fwtty_profile_data(port->stats.writes, c);

        spin_lock_bh(&port->lock);
        n = dma_fifo_in(&port->tx_fifo, buf, c);
        len = dma_fifo_out_level(&port->tx_fifo);
        if (len < DRAIN_THRESHOLD)
                schedule_delayed_work(&port->drain, 1);
        spin_unlock_bh(&port->lock);

        if (len >= DRAIN_THRESHOLD)
                fwtty_tx(port, false);

        debug_short_write(port, c, n);

        return (n < 0) ? 0 : n;
}

static int fwtty_write_room(struct tty_struct *tty)
{
        struct fwtty_port *port = tty->driver_data;
        int n;

        spin_lock_bh(&port->lock);
        n = dma_fifo_avail(&port->tx_fifo);
        spin_unlock_bh(&port->lock);

        fwtty_dbg(port, "%d\n", n);

        return n;
}

static int fwtty_chars_in_buffer(struct tty_struct *tty)
{
        struct fwtty_port *port = tty->driver_data;
        int n;

        spin_lock_bh(&port->lock);
        n = dma_fifo_level(&port->tx_fifo);
        spin_unlock_bh(&port->lock);

        fwtty_dbg(port, "%d\n", n);

        return n;
}

static void fwtty_send_xchar(struct tty_struct *tty, char ch)
{
        struct fwtty_port *port = tty->driver_data;

        fwtty_dbg(port, "%02x\n", ch);

        fwtty_write_xchar(port, ch);
}

static void fwtty_throttle(struct tty_struct *tty)
{
        struct fwtty_port *port = tty->driver_data;

        /*
         * Ignore throttling (but not unthrottling).
         * It only makes sense to throttle when data will no longer be
         * accepted by the tty flip buffer. For example, it is
         * possible for received data to overflow the tty buffer long
         * before the line discipline ever has a chance to throttle the driver.
         * Additionally, the driver may have already completed the I/O
         * but the tty buffer is still emptying, so the line discipline is
         * throttling and unthrottling nothing.
         */

        ++port->stats.throttled;
}

static void fwtty_unthrottle(struct tty_struct *tty)
{
        struct fwtty_port *port = tty->driver_data;

        fwtty_dbg(port, "CRTSCTS: %d\n", C_CRTSCTS(tty) != 0);

        fwtty_profile_fifo(port, port->stats.unthrottle);

        spin_lock_bh(&port->lock);
        port->mctrl &= ~OOB_RX_THROTTLE;
        if (C_CRTSCTS(tty))
                port->mctrl |= TIOCM_RTS;
        __fwtty_write_port_status(port);
        spin_unlock_bh(&port->lock);
}

static int check_msr_delta(struct fwtty_port *port, unsigned long mask,
                           struct async_icount *prev)
{
        struct async_icount now;
        int delta;

        now = port->icount;

        delta = ((mask & TIOCM_RNG && prev->rng != now.rng) ||
                 (mask & TIOCM_DSR && prev->dsr != now.dsr) ||
                 (mask & TIOCM_CAR && prev->dcd != now.dcd) ||
                 (mask & TIOCM_CTS && prev->cts != now.cts));

        *prev = now;

        return delta;
}

static int wait_msr_change(struct fwtty_port *port, unsigned long mask)
{
        struct async_icount prev;

        prev = port->icount;

        return wait_event_interruptible(port->port.delta_msr_wait,
                                        check_msr_delta(port, mask, &prev));
}

static int get_serial_info(struct tty_struct *tty,
                           struct serial_struct *ss)
{
        struct fwtty_port *port = tty->driver_data;

        mutex_lock(&port->port.mutex);
        ss->type =  PORT_UNKNOWN;
        ss->line =  port->port.tty->index;
        ss->flags = port->port.flags;
        ss->xmit_fifo_size = FWTTY_PORT_TXFIFO_LEN;
        ss->baud_base = 400000000;
        ss->close_delay = port->port.close_delay;
        mutex_unlock(&port->port.mutex);
        return 0;
}

static int set_serial_info(struct tty_struct *tty,
                           struct serial_struct *ss)
{
        struct fwtty_port *port = tty->driver_data;

        if (ss->irq != 0 || ss->port != 0 || ss->custom_divisor != 0 ||
            ss->baud_base != 400000000)
                return -EPERM;

        mutex_lock(&port->port.mutex);
        if (!capable(CAP_SYS_ADMIN)) {
                if (((ss->flags & ~ASYNC_USR_MASK) !=
                     (port->port.flags & ~ASYNC_USR_MASK))) {
                        mutex_unlock(&port->port.mutex);
                        return -EPERM;
                }
        }
        port->port.close_delay = ss->close_delay * HZ / 100;
        mutex_unlock(&port->port.mutex);

        return 0;
}

static int fwtty_ioctl(struct tty_struct *tty, unsigned int cmd,
                       unsigned long arg)
{
        struct fwtty_port *port = tty->driver_data;
        int err;

        switch (cmd) {
        case TIOCMIWAIT:
                err = wait_msr_change(port, arg);
                break;

        default:
                err = -ENOIOCTLCMD;
        }

        return err;
}

static void fwtty_set_termios(struct tty_struct *tty, struct ktermios *old)
{
        struct fwtty_port *port = tty->driver_data;
        unsigned int baud;

        spin_lock_bh(&port->lock);
        baud = set_termios(port, tty);

        if ((baud == 0) && (old->c_cflag & CBAUD)) {
                port->mctrl &= ~(TIOCM_DTR | TIOCM_RTS);
        } else if ((baud != 0) && !(old->c_cflag & CBAUD)) {
                if (C_CRTSCTS(tty) || !tty_throttled(tty))
                        port->mctrl |= TIOCM_DTR | TIOCM_RTS;
                else
                        port->mctrl |= TIOCM_DTR;
        }
        __fwtty_write_port_status(port);
        spin_unlock_bh(&port->lock);

        if (old->c_cflag & CRTSCTS) {
                if (!C_CRTSCTS(tty)) {
                        tty->hw_stopped = 0;
                        fwtty_restart_tx(port);
                }
        } else if (C_CRTSCTS(tty) && ~port->mstatus & TIOCM_CTS) {
                tty->hw_stopped = 1;
        }
}

/**
 * fwtty_break_ctl - start/stop sending breaks
 *
 * Signals the remote to start or stop generating simulated breaks.
 * First, stop dequeueing from the fifo and wait for writer/drain to leave tx
 * before signalling the break line status. This guarantees any pending rx will
 * be queued to the line discipline before break is simulated on the remote.
 * Conversely, turning off break_ctl requires signalling the line status change,
 * then enabling tx.
 */
static int fwtty_break_ctl(struct tty_struct *tty, int state)
{
        struct fwtty_port *port = tty->driver_data;
        long ret;

        fwtty_dbg(port, "%d\n", state);

        if (state == -1) {
                set_bit(STOP_TX, &port->flags);
                ret = wait_event_interruptible_timeout(port->wait_tx,
                                               !test_bit(IN_TX, &port->flags),
                                               10);
                if (ret == 0 || ret == -ERESTARTSYS) {
                        clear_bit(STOP_TX, &port->flags);
                        fwtty_restart_tx(port);
                        return -EINTR;
                }
        }

        spin_lock_bh(&port->lock);
        port->break_ctl = (state == -1);
        __fwtty_write_port_status(port);
        spin_unlock_bh(&port->lock);

        if (state == 0) {
                spin_lock_bh(&port->lock);
                dma_fifo_reset(&port->tx_fifo);
                clear_bit(STOP_TX, &port->flags);
                spin_unlock_bh(&port->lock);
        }
        return 0;
}

static int fwtty_tiocmget(struct tty_struct *tty)
{
        struct fwtty_port *port = tty->driver_data;
        unsigned int tiocm;

        spin_lock_bh(&port->lock);
        tiocm = (port->mctrl & MCTRL_MASK) | (port->mstatus & ~MCTRL_MASK);
        spin_unlock_bh(&port->lock);

        fwtty_dbg(port, "%x\n", tiocm);

        return tiocm;
}

static int fwtty_tiocmset(struct tty_struct *tty,
                          unsigned int set, unsigned int clear)
{
        struct fwtty_port *port = tty->driver_data;

        fwtty_dbg(port, "set: %x clear: %x\n", set, clear);

        /* TODO: simulate loopback if TIOCM_LOOP set */

        spin_lock_bh(&port->lock);
        port->mctrl &= ~(clear & MCTRL_MASK & 0xffff);
        port->mctrl |= set & MCTRL_MASK & 0xffff;
        __fwtty_write_port_status(port);
        spin_unlock_bh(&port->lock);
        return 0;
}

static int fwtty_get_icount(struct tty_struct *tty,
                            struct serial_icounter_struct *icount)
{
        struct fwtty_port *port = tty->driver_data;
        struct stats stats;

        memcpy(&stats, &port->stats, sizeof(stats));
        if (port->port.console)
                (*port->fwcon_ops->stats)(&stats, port->con_data);

        icount->cts = port->icount.cts;
        icount->dsr = port->icount.dsr;
        icount->rng = port->icount.rng;
        icount->dcd = port->icount.dcd;
        icount->rx  = port->icount.rx;
        icount->tx  = port->icount.tx + stats.xchars;
        icount->frame   = port->icount.frame;
        icount->overrun = port->icount.overrun;
        icount->parity  = port->icount.parity;
        icount->brk     = port->icount.brk;
        icount->buf_overrun = port->icount.overrun;
        return 0;
}

static void fwtty_proc_show_port(struct seq_file *m, struct fwtty_port *port)
{
        struct stats stats;

        memcpy(&stats, &port->stats, sizeof(stats));
        if (port->port.console)
                (*port->fwcon_ops->stats)(&stats, port->con_data);

        seq_printf(m, " addr:%012llx tx:%d rx:%d", port->rx_handler.offset,
                   port->icount.tx + stats.xchars, port->icount.rx);
        seq_printf(m, " cts:%d dsr:%d rng:%d dcd:%d", port->icount.cts,
                   port->icount.dsr, port->icount.rng, port->icount.dcd);
        seq_printf(m, " fe:%d oe:%d pe:%d brk:%d", port->icount.frame,
                   port->icount.overrun, port->icount.parity, port->icount.brk);
}

static void fwtty_debugfs_show_port(struct seq_file *m, struct fwtty_port *port)
{
        struct stats stats;

        memcpy(&stats, &port->stats, sizeof(stats));
        if (port->port.console)
                (*port->fwcon_ops->stats)(&stats, port->con_data);

        seq_printf(m, " dr:%d st:%d err:%d lost:%d", stats.dropped,
                   stats.tx_stall, stats.fifo_errs, stats.lost);
        seq_printf(m, " pkts:%d thr:%d", stats.sent, stats.throttled);

        if (port->port.console) {
                seq_puts(m, "\n    ");
                (*port->fwcon_ops->proc_show)(m, port->con_data);
        }

        fwtty_dump_profile(m, &port->stats);
}

static void fwtty_debugfs_show_peer(struct seq_file *m, struct fwtty_peer *peer)
{
        int generation = peer->generation;

        smp_rmb();
        seq_printf(m, " %s:", dev_name(&peer->unit->device));
        seq_printf(m, " node:%04x gen:%d", peer->node_id, generation);
        seq_printf(m, " sp:%d max:%d guid:%016llx", peer->speed,
                   peer->max_payload, (unsigned long long)peer->guid);
        seq_printf(m, " mgmt:%012llx", (unsigned long long)peer->mgmt_addr);
        seq_printf(m, " addr:%012llx", (unsigned long long)peer->status_addr);
        seq_putc(m, '\n');
}

static int fwtty_proc_show(struct seq_file *m, void *v)
{
        struct fwtty_port *port;
        int i;

        seq_puts(m, "fwserinfo: 1.0 driver: 1.0\n");
        for (i = 0; i < MAX_TOTAL_PORTS && (port = fwtty_port_get(i)); ++i) {
                seq_printf(m, "%2d:", i);
                if (capable(CAP_SYS_ADMIN))
                        fwtty_proc_show_port(m, port);
                fwtty_port_put(port);
                seq_puts(m, "\n");
        }
        return 0;
}

static int fwtty_stats_show(struct seq_file *m, void *v)
{
        struct fw_serial *serial = m->private;
        struct fwtty_port *port;
        int i;

        for (i = 0; i < num_ports; ++i) {
                port = fwtty_port_get(serial->ports[i]->index);
                if (port) {
                        seq_printf(m, "%2d:", port->index);
                        fwtty_proc_show_port(m, port);
                        fwtty_debugfs_show_port(m, port);
                        fwtty_port_put(port);
                        seq_puts(m, "\n");
                }
        }
        return 0;
}
DEFINE_SHOW_ATTRIBUTE(fwtty_stats);

static int fwtty_peers_show(struct seq_file *m, void *v)
{
        struct fw_serial *serial = m->private;
        struct fwtty_peer *peer;

        rcu_read_lock();
        seq_printf(m, "card: %s  guid: %016llx\n",
                   dev_name(serial->card->device),
                   (unsigned long long)serial->card->guid);
        list_for_each_entry_rcu(peer, &serial->peer_list, list)
                fwtty_debugfs_show_peer(m, peer);
        rcu_read_unlock();
        return 0;
}
DEFINE_SHOW_ATTRIBUTE(fwtty_peers);

static const struct tty_port_operations fwtty_port_ops = {
        .dtr_rts =              fwtty_port_dtr_rts,
        .carrier_raised =       fwtty_port_carrier_raised,
        .shutdown =             fwtty_port_shutdown,
        .activate =             fwtty_port_activate,
};

static const struct tty_operations fwtty_ops = {
        .open =                 fwtty_open,
        .close =                fwtty_close,
        .hangup =               fwtty_hangup,
        .cleanup =              fwtty_cleanup,
        .install =              fwtty_install,
        .write =                fwtty_write,
        .write_room =           fwtty_write_room,
        .chars_in_buffer =      fwtty_chars_in_buffer,
        .send_xchar =           fwtty_send_xchar,
        .throttle =             fwtty_throttle,
        .unthrottle =           fwtty_unthrottle,
        .ioctl =                fwtty_ioctl,
        .set_termios =          fwtty_set_termios,
        .break_ctl =            fwtty_break_ctl,
        .tiocmget =             fwtty_tiocmget,
        .tiocmset =             fwtty_tiocmset,
        .get_icount =           fwtty_get_icount,
        .set_serial =           set_serial_info,
        .get_serial =           get_serial_info,
        .proc_show =            fwtty_proc_show,
};

static const struct tty_operations fwloop_ops = {
        .open =                 fwtty_open,
        .close =                fwtty_close,
        .hangup =               fwtty_hangup,
        .cleanup =              fwtty_cleanup,
        .install =              fwloop_install,
        .write =                fwtty_write,
        .write_room =           fwtty_write_room,
        .chars_in_buffer =      fwtty_chars_in_buffer,
        .send_xchar =           fwtty_send_xchar,
        .throttle =             fwtty_throttle,
        .unthrottle =           fwtty_unthrottle,
        .ioctl =                fwtty_ioctl,
        .set_termios =          fwtty_set_termios,
        .break_ctl =            fwtty_break_ctl,
        .tiocmget =             fwtty_tiocmget,
        .tiocmset =             fwtty_tiocmset,
        .get_icount =           fwtty_get_icount,
        .set_serial =           set_serial_info,
        .get_serial =           get_serial_info,
};

static inline int mgmt_pkt_expected_len(__be16 code)
{
        static const struct fwserial_mgmt_pkt pkt;

        switch (be16_to_cpu(code)) {
        case FWSC_VIRT_CABLE_PLUG:
                return sizeof(pkt.hdr) + sizeof(pkt.plug_req);

        case FWSC_VIRT_CABLE_PLUG_RSP:  /* | FWSC_RSP_OK */
                return sizeof(pkt.hdr) + sizeof(pkt.plug_rsp);

        case FWSC_VIRT_CABLE_UNPLUG:
        case FWSC_VIRT_CABLE_UNPLUG_RSP:
        case FWSC_VIRT_CABLE_PLUG_RSP | FWSC_RSP_NACK:
        case FWSC_VIRT_CABLE_UNPLUG_RSP | FWSC_RSP_NACK:
                return sizeof(pkt.hdr);

        default:
                return -1;
        }
}

static inline void fill_plug_params(struct virt_plug_params *params,
                                    struct fwtty_port *port)
{
        u64 status_addr = port->rx_handler.offset;
        u64 fifo_addr = port->rx_handler.offset + 4;
        size_t fifo_len = port->rx_handler.length - 4;

        params->status_hi = cpu_to_be32(status_addr >> 32);
        params->status_lo = cpu_to_be32(status_addr);
        params->fifo_hi = cpu_to_be32(fifo_addr >> 32);
        params->fifo_lo = cpu_to_be32(fifo_addr);
        params->fifo_len = cpu_to_be32(fifo_len);
}

static inline void fill_plug_req(struct fwserial_mgmt_pkt *pkt,
                                 struct fwtty_port *port)
{
        pkt->hdr.code = cpu_to_be16(FWSC_VIRT_CABLE_PLUG);
        pkt->hdr.len = cpu_to_be16(mgmt_pkt_expected_len(pkt->hdr.code));
        fill_plug_params(&pkt->plug_req, port);
}

static inline void fill_plug_rsp_ok(struct fwserial_mgmt_pkt *pkt,
                                    struct fwtty_port *port)
{
        pkt->hdr.code = cpu_to_be16(FWSC_VIRT_CABLE_PLUG_RSP);
        pkt->hdr.len = cpu_to_be16(mgmt_pkt_expected_len(pkt->hdr.code));
        fill_plug_params(&pkt->plug_rsp, port);
}

static inline void fill_plug_rsp_nack(struct fwserial_mgmt_pkt *pkt)
{
        pkt->hdr.code = cpu_to_be16(FWSC_VIRT_CABLE_PLUG_RSP | FWSC_RSP_NACK);
        pkt->hdr.len = cpu_to_be16(mgmt_pkt_expected_len(pkt->hdr.code));
}

static inline void fill_unplug_rsp_nack(struct fwserial_mgmt_pkt *pkt)
{
        pkt->hdr.code = cpu_to_be16(FWSC_VIRT_CABLE_UNPLUG_RSP | FWSC_RSP_NACK);
        pkt->hdr.len = cpu_to_be16(mgmt_pkt_expected_len(pkt->hdr.code));
}

static inline void fill_unplug_rsp_ok(struct fwserial_mgmt_pkt *pkt)
{
        pkt->hdr.code = cpu_to_be16(FWSC_VIRT_CABLE_UNPLUG_RSP);
        pkt->hdr.len = cpu_to_be16(mgmt_pkt_expected_len(pkt->hdr.code));
}

static void fwserial_virt_plug_complete(struct fwtty_peer *peer,
                                        struct virt_plug_params *params)
{
        struct fwtty_port *port = peer->port;

        peer->status_addr = be32_to_u64(params->status_hi, params->status_lo);
        peer->fifo_addr = be32_to_u64(params->fifo_hi, params->fifo_lo);
        peer->fifo_len = be32_to_cpu(params->fifo_len);
        peer_set_state(peer, FWPS_ATTACHED);

        /* reconfigure tx_fifo optimally for this peer */
        spin_lock_bh(&port->lock);
        port->max_payload = min(peer->max_payload, peer->fifo_len);
        dma_fifo_change_tx_limit(&port->tx_fifo, port->max_payload);
        spin_unlock_bh(&peer->port->lock);

        if (port->port.console && port->fwcon_ops->notify)
                (*port->fwcon_ops->notify)(FWCON_NOTIFY_ATTACH, port->con_data);

        fwtty_info(&peer->unit, "peer (guid:%016llx) connected on %s\n",
                   (unsigned long long)peer->guid, dev_name(port->device));
}

static inline int fwserial_send_mgmt_sync(struct fwtty_peer *peer,
                                          struct fwserial_mgmt_pkt *pkt)
{
        int generation;
        int rcode, tries = 5;

        do {
                generation = peer->generation;
                smp_rmb();

                rcode = fw_run_transaction(peer->serial->card,
                                           TCODE_WRITE_BLOCK_REQUEST,
                                           peer->node_id,
                                           generation, peer->speed,
                                           peer->mgmt_addr,
                                           pkt, be16_to_cpu(pkt->hdr.len));
                if (rcode == RCODE_BUSY || rcode == RCODE_SEND_ERROR ||
                    rcode == RCODE_GENERATION) {
                        fwtty_dbg(&peer->unit, "mgmt write error: %d\n", rcode);
                        continue;
                } else {
                        break;
                }
        } while (--tries > 0);
        return rcode;
}

/**
 * fwserial_claim_port - attempt to claim port @ index for peer
 *
 * Returns ptr to claimed port or error code (as ERR_PTR())
 * Can sleep - must be called from process context
 */
static struct fwtty_port *fwserial_claim_port(struct fwtty_peer *peer,
                                              int index)
{
        struct fwtty_port *port;

        if (index < 0 || index >= num_ports)
                return ERR_PTR(-EINVAL);

        /* must guarantee that previous port releases have completed */
        synchronize_rcu();

        port = peer->serial->ports[index];
        spin_lock_bh(&port->lock);
        if (!rcu_access_pointer(port->peer))
                rcu_assign_pointer(port->peer, peer);
        else
                port = ERR_PTR(-EBUSY);
        spin_unlock_bh(&port->lock);

        return port;
}

/**
 * fwserial_find_port - find avail port and claim for peer
 *
 * Returns ptr to claimed port or NULL if none avail
 * Can sleep - must be called from process context
 */
static struct fwtty_port *fwserial_find_port(struct fwtty_peer *peer)
{
        struct fwtty_port **ports = peer->serial->ports;
        int i;

        /* must guarantee that previous port releases have completed */
        synchronize_rcu();

        /* TODO: implement optional GUID-to-specific port # matching */

        /* find an unattached port (but not the loopback port, if present) */
        for (i = 0; i < num_ttys; ++i) {
                spin_lock_bh(&ports[i]->lock);
                if (!ports[i]->peer) {
                        /* claim port */
                        rcu_assign_pointer(ports[i]->peer, peer);
                        spin_unlock_bh(&ports[i]->lock);
                        return ports[i];
                }
                spin_unlock_bh(&ports[i]->lock);
        }
        return NULL;
}

static void fwserial_release_port(struct fwtty_port *port, bool reset)
{
        /* drop carrier (and all other line status) */
        if (reset)
                fwtty_update_port_status(port, 0);

        spin_lock_bh(&port->lock);

        /* reset dma fifo max transmission size back to S100 */
        port->max_payload = link_speed_to_max_payload(SCODE_100);
        dma_fifo_change_tx_limit(&port->tx_fifo, port->max_payload);

        RCU_INIT_POINTER(port->peer, NULL);
        spin_unlock_bh(&port->lock);

        if (port->port.console && port->fwcon_ops->notify)
                (*port->fwcon_ops->notify)(FWCON_NOTIFY_DETACH, port->con_data);
}

static void fwserial_plug_timeout(struct timer_list *t)
{
        struct fwtty_peer *peer = from_timer(peer, t, timer);
        struct fwtty_port *port;

        spin_lock_bh(&peer->lock);
        if (peer->state != FWPS_PLUG_PENDING) {
                spin_unlock_bh(&peer->lock);
                return;
        }

        port = peer_revert_state(peer);
        spin_unlock_bh(&peer->lock);

        if (port)
                fwserial_release_port(port, false);
}

/**
 * fwserial_connect_peer - initiate virtual cable with peer
 *
 * Returns 0 if VIRT_CABLE_PLUG request was successfully sent,
 * otherwise error code.  Must be called from process context.
 */
static int fwserial_connect_peer(struct fwtty_peer *peer)
{
        struct fwtty_port *port;
        struct fwserial_mgmt_pkt *pkt;
        int err, rcode;

        pkt = kmalloc(sizeof(*pkt), GFP_KERNEL);
        if (!pkt)
                return -ENOMEM;

        port = fwserial_find_port(peer);
        if (!port) {
                fwtty_err(&peer->unit, "avail ports in use\n");
                err = -EBUSY;
                goto free_pkt;
        }

        spin_lock_bh(&peer->lock);

        /* only initiate VIRT_CABLE_PLUG if peer is currently not attached */
        if (peer->state != FWPS_NOT_ATTACHED) {
                err = -EBUSY;
                goto release_port;
        }

        peer->port = port;
        peer_set_state(peer, FWPS_PLUG_PENDING);

        fill_plug_req(pkt, peer->port);

        mod_timer(&peer->timer, jiffies + VIRT_CABLE_PLUG_TIMEOUT);
        spin_unlock_bh(&peer->lock);

        rcode = fwserial_send_mgmt_sync(peer, pkt);

        spin_lock_bh(&peer->lock);
        if (peer->state == FWPS_PLUG_PENDING && rcode != RCODE_COMPLETE) {
                if (rcode == RCODE_CONFLICT_ERROR)
                        err = -EAGAIN;
                else
                        err = -EIO;
                goto cancel_timer;
        }
        spin_unlock_bh(&peer->lock);

        kfree(pkt);
        return 0;

cancel_timer:
        del_timer(&peer->timer);
        peer_revert_state(peer);
release_port:
        spin_unlock_bh(&peer->lock);
        fwserial_release_port(port, false);
free_pkt:
        kfree(pkt);
        return err;
}

/**
 * fwserial_close_port -
 * HUP the tty (if the tty exists) and unregister the tty device.
 * Only used by the unit driver upon unit removal to disconnect and
 * cleanup all attached ports
 *
 * The port reference is put by fwtty_cleanup (if a reference was
 * ever taken).
 */
static void fwserial_close_port(struct tty_driver *driver,
                                struct fwtty_port *port)
{
        struct tty_struct *tty;

        mutex_lock(&port->port.mutex);
        tty = tty_port_tty_get(&port->port);
        if (tty) {
                tty_vhangup(tty);
                tty_kref_put(tty);
        }
        mutex_unlock(&port->port.mutex);

        if (driver == fwloop_driver)
                tty_unregister_device(driver, loop_idx(port));
        else
                tty_unregister_device(driver, port->index);
}

/**
 * fwserial_lookup - finds first fw_serial associated with card
 * @card: fw_card to match
 *
 * NB: caller must be holding fwserial_list_mutex
 */
static struct fw_serial *fwserial_lookup(struct fw_card *card)
{
        struct fw_serial *serial;

        list_for_each_entry(serial, &fwserial_list, list) {
                if (card == serial->card)
                        return serial;
        }

        return NULL;
}

/**
 * __fwserial_lookup_rcu - finds first fw_serial associated with card
 * @card: fw_card to match
 *
 * NB: caller must be inside rcu_read_lock() section
 */
static struct fw_serial *__fwserial_lookup_rcu(struct fw_card *card)
{
        struct fw_serial *serial;

        list_for_each_entry_rcu(serial, &fwserial_list, list) {
                if (card == serial->card)
                        return serial;
        }

        return NULL;
}

/**
 * __fwserial_peer_by_node_id - finds a peer matching the given generation + id
 *
 * If a matching peer could not be found for the specified generation/node id,
 * this could be because:
 * a) the generation has changed and one of the nodes hasn't updated yet
 * b) the remote node has created its remote unit device before this
 *    local node has created its corresponding remote unit device
 * In either case, the remote node should retry
 *
 * Note: caller must be in rcu_read_lock() section
 */
static struct fwtty_peer *__fwserial_peer_by_node_id(struct fw_card *card,
                                                     int generation, int id)
{
        struct fw_serial *serial;
        struct fwtty_peer *peer;

        serial = __fwserial_lookup_rcu(card);
        if (!serial) {
                /*
                 * Something is very wrong - there should be a matching
                 * fw_serial structure for every fw_card. Maybe the remote node
                 * has created its remote unit device before this driver has
                 * been probed for any unit devices...
                 */
                fwtty_err(card, "unknown card (guid %016llx)\n",
                          (unsigned long long)card->guid);
                return NULL;
        }

        list_for_each_entry_rcu(peer, &serial->peer_list, list) {
                int g = peer->generation;

                smp_rmb();
                if (generation == g && id == peer->node_id)
                        return peer;
        }

        return NULL;
}

#ifdef DEBUG
static void __dump_peer_list(struct fw_card *card)
{
        struct fw_serial *serial;
        struct fwtty_peer *peer;

        serial = __fwserial_lookup_rcu(card);
        if (!serial)
                return;

        list_for_each_entry_rcu(peer, &serial->peer_list, list) {
                int g = peer->generation;

                smp_rmb();
                fwtty_dbg(card, "peer(%d:%x) guid: %016llx\n",
                          g, peer->node_id, (unsigned long long)peer->guid);
        }
}
#else
#define __dump_peer_list(s)
#endif

static void fwserial_auto_connect(struct work_struct *work)
{
        struct fwtty_peer *peer = to_peer(to_delayed_work(work), connect);
        int err;

        err = fwserial_connect_peer(peer);
        if (err == -EAGAIN && ++peer->connect_retries < MAX_CONNECT_RETRIES)
                schedule_delayed_work(&peer->connect, CONNECT_RETRY_DELAY);
}

static void fwserial_peer_workfn(struct work_struct *work)
{
        struct fwtty_peer *peer = to_peer(work, work);

        peer->workfn(work);
}

/**
 * fwserial_add_peer - add a newly probed 'serial' unit device as a 'peer'
 * @serial: aggregate representing the specific fw_card to add the peer to
 * @unit: 'peer' to create and add to peer_list of serial
 *
 * Adds a 'peer' (ie, a local or remote 'serial' unit device) to the list of
 * peers for a specific fw_card. Optionally, auto-attach this peer to an
 * available tty port. This function is called either directly or indirectly
 * as a result of a 'serial' unit device being created & probed.
 *
 * Note: this function is serialized with fwserial_remove_peer() by the
 * fwserial_list_mutex held in fwserial_probe().
 *
 * A 1:1 correspondence between an fw_unit and an fwtty_peer is maintained
 * via the dev_set_drvdata() for the device of the fw_unit.
 */
static int fwserial_add_peer(struct fw_serial *serial, struct fw_unit *unit)
{
        struct device *dev = &unit->device;
        struct fw_device  *parent = fw_parent_device(unit);
        struct fwtty_peer *peer;
        struct fw_csr_iterator ci;
        int key, val;

        int generation;

        peer = kzalloc(sizeof(*peer), GFP_KERNEL);
        if (!peer)
                return -ENOMEM;

        peer_set_state(peer, FWPS_NOT_ATTACHED);

        dev_set_drvdata(dev, peer);
        peer->unit = unit;
        peer->guid = (u64)parent->config_rom[3] << 32 | parent->config_rom[4];
        peer->speed = parent->max_speed;
        peer->max_payload = min(device_max_receive(parent),
                                link_speed_to_max_payload(peer->speed));

        generation = parent->generation;
        smp_rmb();
        peer->node_id = parent->node_id;
        smp_wmb();
        peer->generation = generation;

        /* retrieve the mgmt bus addr from the unit directory */
        fw_csr_iterator_init(&ci, unit->directory);
        while (fw_csr_iterator_next(&ci, &key, &val)) {
                if (key == (CSR_OFFSET | CSR_DEPENDENT_INFO)) {
                        peer->mgmt_addr = CSR_REGISTER_BASE + 4 * val;
                        break;
                }
        }
        if (peer->mgmt_addr == 0ULL) {
                /*
                 * No mgmt address effectively disables VIRT_CABLE_PLUG -
                 * this peer will not be able to attach to a remote
                 */
                peer_set_state(peer, FWPS_NO_MGMT_ADDR);
        }

        spin_lock_init(&peer->lock);
        peer->port = NULL;

        timer_setup(&peer->timer, fwserial_plug_timeout, 0);
        INIT_WORK(&peer->work, fwserial_peer_workfn);
        INIT_DELAYED_WORK(&peer->connect, fwserial_auto_connect);

        /* associate peer with specific fw_card */
        peer->serial = serial;
        list_add_rcu(&peer->list, &serial->peer_list);

        fwtty_info(&peer->unit, "peer added (guid:%016llx)\n",
                   (unsigned long long)peer->guid);

        /* identify the local unit & virt cable to loopback port */
        if (parent->is_local) {
                serial->self = peer;
                if (create_loop_dev) {
                        struct fwtty_port *port;

                        port = fwserial_claim_port(peer, num_ttys);
                        if (!IS_ERR(port)) {
                                struct virt_plug_params params;

                                spin_lock_bh(&peer->lock);
                                peer->port = port;
                                fill_plug_params(&params, port);
                                fwserial_virt_plug_complete(peer, &params);
                                spin_unlock_bh(&peer->lock);

                                fwtty_write_port_status(port);
                        }
                }

        } else if (auto_connect) {
                /* auto-attach to remote units only (if policy allows) */
                schedule_delayed_work(&peer->connect, 1);
        }

        return 0;
}

/**
 * fwserial_remove_peer - remove a 'serial' unit device as a 'peer'
 *
 * Remove a 'peer' from its list of peers. This function is only
 * called by fwserial_remove() on bus removal of the unit device.
 *
 * Note: this function is serialized with fwserial_add_peer() by the
 * fwserial_list_mutex held in fwserial_remove().
 */
static void fwserial_remove_peer(struct fwtty_peer *peer)
{
        struct fwtty_port *port;

        spin_lock_bh(&peer->lock);
        peer_set_state(peer, FWPS_GONE);
        spin_unlock_bh(&peer->lock);

        cancel_delayed_work_sync(&peer->connect);
        cancel_work_sync(&peer->work);

        spin_lock_bh(&peer->lock);
        /* if this unit is the local unit, clear link */
        if (peer == peer->serial->self)
                peer->serial->self = NULL;

        /* cancel the request timeout timer (if running) */
        del_timer(&peer->timer);

        port = peer->port;
        peer->port = NULL;

        list_del_rcu(&peer->list);

        fwtty_info(&peer->unit, "peer removed (guid:%016llx)\n",
                   (unsigned long long)peer->guid);

        spin_unlock_bh(&peer->lock);

        if (port)
                fwserial_release_port(port, true);

        synchronize_rcu();
        kfree(peer);
}

/**
 * fwserial_create - init everything to create TTYs for a specific fw_card
 * @unit: fw_unit for first 'serial' unit device probed for this fw_card
 *
 * This function inits the aggregate structure (an fw_serial instance)
 * used to manage the TTY ports registered by a specific fw_card. Also, the
 * unit device is added as the first 'peer'.
 *
 * This unit device may represent a local unit device (as specified by the
 * config ROM unit directory) or it may represent a remote unit device
 * (as specified by the reading of the remote node's config ROM).
 *
 * Returns 0 to indicate "ownership" of the unit device, or a negative errno
 * value to indicate which error.
 */
static int fwserial_create(struct fw_unit *unit)
{
        struct fw_device *parent = fw_parent_device(unit);
        struct fw_card *card = parent->card;
        struct fw_serial *serial;
        struct fwtty_port *port;
        struct device *tty_dev;
        int i, j;
        int err;

        serial = kzalloc(sizeof(*serial), GFP_KERNEL);
        if (!serial)
                return -ENOMEM;

        kref_init(&serial->kref);
        serial->card = card;
        INIT_LIST_HEAD(&serial->peer_list);

        for (i = 0; i < num_ports; ++i) {
                port = kzalloc(sizeof(*port), GFP_KERNEL);
                if (!port) {
                        err = -ENOMEM;
                        goto free_ports;
                }
                tty_port_init(&port->port);
                port->index = FWTTY_INVALID_INDEX;
                port->port.ops = &fwtty_port_ops;
                port->serial = serial;
                tty_buffer_set_limit(&port->port, 128 * 1024);

                spin_lock_init(&port->lock);
                INIT_DELAYED_WORK(&port->drain, fwtty_drain_tx);
                INIT_DELAYED_WORK(&port->emit_breaks, fwtty_emit_breaks);
                INIT_WORK(&port->hangup, fwtty_do_hangup);
                init_waitqueue_head(&port->wait_tx);
                port->max_payload = link_speed_to_max_payload(SCODE_100);
                dma_fifo_init(&port->tx_fifo);

                RCU_INIT_POINTER(port->peer, NULL);
                serial->ports[i] = port;

                /* get unique bus addr region for port's status & recv fifo */
                port->rx_handler.length = FWTTY_PORT_RXFIFO_LEN + 4;
                port->rx_handler.address_callback = fwtty_port_handler;
                port->rx_handler.callback_data = port;
                /*
                 * XXX: use custom memory region above cpu physical memory addrs
                 * this will ease porting to 64-bit firewire adapters
                 */
                err = fw_core_add_address_handler(&port->rx_handler,
                                                  &fw_high_memory_region);
                if (err) {
                        kfree(port);
                        goto free_ports;
                }
        }
        /* preserve i for error cleanup */

        err = fwtty_ports_add(serial);
        if (err) {
                fwtty_err(&unit, "no space in port table\n");
                goto free_ports;
        }

        for (j = 0; j < num_ttys; ++j) {
                tty_dev = tty_port_register_device(&serial->ports[j]->port,
                                                   fwtty_driver,
                                                   serial->ports[j]->index,
                                                   card->device);
                if (IS_ERR(tty_dev)) {
                        err = PTR_ERR(tty_dev);
                        fwtty_err(&unit, "register tty device error (%d)\n",
                                  err);
                        goto unregister_ttys;
                }

                serial->ports[j]->device = tty_dev;
        }
        /* preserve j for error cleanup */

        if (create_loop_dev) {
                struct device *loop_dev;

                loop_dev = tty_port_register_device(&serial->ports[j]->port,
                                                    fwloop_driver,
                                                    loop_idx(serial->ports[j]),
                                                    card->device);
                if (IS_ERR(loop_dev)) {
                        err = PTR_ERR(loop_dev);
                        fwtty_err(&unit, "create loop device failed (%d)\n",
                                  err);
                        goto unregister_ttys;
                }
                serial->ports[j]->device = loop_dev;
                serial->ports[j]->loopback = true;
        }

        if (!IS_ERR_OR_NULL(fwserial_debugfs)) {
                serial->debugfs = debugfs_create_dir(dev_name(&unit->device),
                                                     fwserial_debugfs);
                if (!IS_ERR_OR_NULL(serial->debugfs)) {
                        debugfs_create_file("peers", 0444, serial->debugfs,
                                            serial, &fwtty_peers_fops);
                        debugfs_create_file("stats", 0444, serial->debugfs,
                                            serial, &fwtty_stats_fops);
                }
        }

        list_add_rcu(&serial->list, &fwserial_list);

        fwtty_notice(&unit, "TTY over FireWire on device %s (guid %016llx)\n",
                     dev_name(card->device), (unsigned long long)card->guid);

        err = fwserial_add_peer(serial, unit);
        if (!err)
                return 0;

        fwtty_err(&unit, "unable to add peer unit device (%d)\n", err);

        /* fall-through to error processing */
        debugfs_remove_recursive(serial->debugfs);

        list_del_rcu(&serial->list);
        if (create_loop_dev)
                tty_unregister_device(fwloop_driver,
                                      loop_idx(serial->ports[j]));
unregister_ttys:
        for (--j; j >= 0; --j)
                tty_unregister_device(fwtty_driver, serial->ports[j]->index);
        kref_put(&serial->kref, fwserial_destroy);
        return err;

free_ports:
        for (--i; i >= 0; --i) {
                tty_port_destroy(&serial->ports[i]->port);
                kfree(serial->ports[i]);
        }
        kfree(serial);
        return err;
}

/**
 * fwserial_probe: bus probe function for firewire 'serial' unit devices
 *
 * A 'serial' unit device is created and probed as a result of:
 * - declaring a ieee1394 bus id table for 'devices' matching a fabricated
 *   'serial' unit specifier id
 * - adding a unit directory to the config ROM(s) for a 'serial' unit
 *
 * The firewire core registers unit devices by enumerating unit directories
 * of a node's config ROM after reading the config ROM when a new node is
 * added to the bus topology after a bus reset.
 *
 * The practical implications of this are:
 * - this probe is called for both local and remote nodes that have a 'serial'
 *   unit directory in their config ROM (that matches the specifiers in
 *   fwserial_id_table).
 * - no specific order is enforced for local vs. remote unit devices
 *
 * This unit driver copes with the lack of specific order in the same way the
 * firewire net driver does -- each probe, for either a local or remote unit
 * device, is treated as a 'peer' (has a struct fwtty_peer instance) and the
 * first peer created for a given fw_card (tracked by the global fwserial_list)
 * creates the underlying TTYs (aggregated in a fw_serial instance).
 *
 * NB: an early attempt to differentiate local & remote unit devices by creating
 *     peers only for remote units and fw_serial instances (with their
 *     associated TTY devices) only for local units was discarded. Managing
 *     the peer lifetimes on device removal proved too complicated.
 *
 * fwserial_probe/fwserial_remove are effectively serialized by the
 * fwserial_list_mutex. This is necessary because the addition of the first peer
 * for a given fw_card will trigger the creation of the fw_serial for that
 * fw_card, which must not simultaneously contend with the removal of the
 * last peer for a given fw_card triggering the destruction of the same
 * fw_serial for the same fw_card.
 */
static int fwserial_probe(struct fw_unit *unit,
                          const struct ieee1394_device_id *id)
{
        struct fw_serial *serial;
        int err;

        mutex_lock(&fwserial_list_mutex);
        serial = fwserial_lookup(fw_parent_device(unit)->card);
        if (!serial)
                err = fwserial_create(unit);
        else
                err = fwserial_add_peer(serial, unit);
        mutex_unlock(&fwserial_list_mutex);
        return err;
}

/**
 * fwserial_remove: bus removal function for firewire 'serial' unit devices
 *
 * The corresponding 'peer' for this unit device is removed from the list of
 * peers for the associated fw_serial (which has a 1:1 correspondence with a
 * specific fw_card). If this is the last peer being removed, then trigger
 * the destruction of the underlying TTYs.
 */
static void fwserial_remove(struct fw_unit *unit)
{
        struct fwtty_peer *peer = dev_get_drvdata(&unit->device);
        struct fw_serial *serial = peer->serial;
        int i;

        mutex_lock(&fwserial_list_mutex);
        fwserial_remove_peer(peer);

        if (list_empty(&serial->peer_list)) {
                /* unlink from the fwserial_list here */
                list_del_rcu(&serial->list);

                debugfs_remove_recursive(serial->debugfs);

                for (i = 0; i < num_ttys; ++i)
                        fwserial_close_port(fwtty_driver, serial->ports[i]);
                if (create_loop_dev)
                        fwserial_close_port(fwloop_driver, serial->ports[i]);
                kref_put(&serial->kref, fwserial_destroy);
        }
        mutex_unlock(&fwserial_list_mutex);
}

/**
 * fwserial_update: bus update function for 'firewire' serial unit devices
 *
 * Updates the new node_id and bus generation for this peer. Note that locking
 * is unnecessary; but careful memory barrier usage is important to enforce the
 * load and store order of generation & node_id.
 *
 * The fw-core orders the write of node_id before generation in the parent
 * fw_device to ensure that a stale node_id cannot be used with a current
 * bus generation. So the generation value must be read before the node_id.
 *
 * In turn, this orders the write of node_id before generation in the peer to
 * also ensure a stale node_id cannot be used with a current bus generation.
 */
static void fwserial_update(struct fw_unit *unit)
{
        struct fw_device *parent = fw_parent_device(unit);
        struct fwtty_peer *peer = dev_get_drvdata(&unit->device);
        int generation;

        generation = parent->generation;
        smp_rmb();
        peer->node_id = parent->node_id;
        smp_wmb();
        peer->generation = generation;
}

static const struct ieee1394_device_id fwserial_id_table[] = {
        {
                .match_flags  = IEEE1394_MATCH_SPECIFIER_ID |
                                IEEE1394_MATCH_VERSION,
                .specifier_id = LINUX_VENDOR_ID,
                .version      = FWSERIAL_VERSION,
        },
        { }
};

static struct fw_driver fwserial_driver = {
        .driver = {
                .owner  = THIS_MODULE,
                .name   = KBUILD_MODNAME,
                .bus    = &fw_bus_type,
        },
        .probe    = fwserial_probe,
        .update   = fwserial_update,
        .remove   = fwserial_remove,
        .id_table = fwserial_id_table,
};

#define FW_UNIT_SPECIFIER(id)   ((CSR_SPECIFIER_ID << 24) | (id))
#define FW_UNIT_VERSION(ver)    ((CSR_VERSION << 24) | (ver))
#define FW_UNIT_ADDRESS(ofs)    (((CSR_OFFSET | CSR_DEPENDENT_INFO) << 24)  \
                                 | (((ofs) - CSR_REGISTER_BASE) >> 2))
/* XXX: config ROM definitons could be improved with semi-automated offset
 * and length calculation
 */
#define FW_ROM_LEN(quads)       ((quads) << 16)
#define FW_ROM_DESCRIPTOR(ofs)  (((CSR_LEAF | CSR_DESCRIPTOR) << 24) | (ofs))

struct fwserial_unit_directory_data {
        u32     len_crc;
        u32     unit_specifier;
        u32     unit_sw_version;
        u32     unit_addr_offset;
        u32     desc1_ofs;
        u32     desc1_len_crc;
        u32     desc1_data[5];
} __packed;

static struct fwserial_unit_directory_data fwserial_unit_directory_data = {
        .len_crc = FW_ROM_LEN(4),
        .unit_specifier = FW_UNIT_SPECIFIER(LINUX_VENDOR_ID),
        .unit_sw_version = FW_UNIT_VERSION(FWSERIAL_VERSION),
        .desc1_ofs = FW_ROM_DESCRIPTOR(1),
        .desc1_len_crc = FW_ROM_LEN(5),
        .desc1_data = {
                0x00000000,                     /*   type = text            */
                0x00000000,                     /*   enc = ASCII, lang EN   */
                0x4c696e75,                     /* 'Linux TTY'              */
                0x78205454,
                0x59000000,
        },
};

static struct fw_descriptor fwserial_unit_directory = {
        .length = sizeof(fwserial_unit_directory_data) / sizeof(u32),
        .key    = (CSR_DIRECTORY | CSR_UNIT) << 24,
        .data   = (u32 *)&fwserial_unit_directory_data,
};

/*
 * The management address is in the unit space region but above other known
 * address users (to keep wild writes from causing havoc)
 */
static const struct fw_address_region fwserial_mgmt_addr_region = {
        .start = CSR_REGISTER_BASE + 0x1e0000ULL,
        .end = 0x1000000000000ULL,
};

static struct fw_address_handler fwserial_mgmt_addr_handler;

/**
 * fwserial_handle_plug_req - handle VIRT_CABLE_PLUG request work
 * @work: ptr to peer->work
 *
 * Attempts to complete the VIRT_CABLE_PLUG handshake sequence for this peer.
 *
 * This checks for a collided request-- ie, that a VIRT_CABLE_PLUG request was
 * already sent to this peer. If so, the collision is resolved by comparing
 * guid values; the loser sends the plug response.
 *
 * Note: if an error prevents a response, don't do anything -- the
 * remote will timeout its request.
 */
static void fwserial_handle_plug_req(struct work_struct *work)
{
        struct fwtty_peer *peer = to_peer(work, work);
        struct virt_plug_params *plug_req = &peer->work_params.plug_req;
        struct fwtty_port *port;
        struct fwserial_mgmt_pkt *pkt;
        int rcode;

        pkt = kmalloc(sizeof(*pkt), GFP_KERNEL);
        if (!pkt)
                return;

        port = fwserial_find_port(peer);

        spin_lock_bh(&peer->lock);

        switch (peer->state) {
        case FWPS_NOT_ATTACHED:
                if (!port) {
                        fwtty_err(&peer->unit, "no more ports avail\n");
                        fill_plug_rsp_nack(pkt);
                } else {
                        peer->port = port;
                        fill_plug_rsp_ok(pkt, peer->port);
                        peer_set_state(peer, FWPS_PLUG_RESPONDING);
                        /* don't release claimed port */
                        port = NULL;
                }
                break;

        case FWPS_PLUG_PENDING:
                if (peer->serial->card->guid > peer->guid)
                        goto cleanup;

                /* We lost - hijack the already-claimed port and send ok */
                del_timer(&peer->timer);
                fill_plug_rsp_ok(pkt, peer->port);
                peer_set_state(peer, FWPS_PLUG_RESPONDING);
                break;

        default:
                fill_plug_rsp_nack(pkt);
        }

        spin_unlock_bh(&peer->lock);
        if (port)
                fwserial_release_port(port, false);

        rcode = fwserial_send_mgmt_sync(peer, pkt);

        spin_lock_bh(&peer->lock);
        if (peer->state == FWPS_PLUG_RESPONDING) {
                if (rcode == RCODE_COMPLETE) {
                        struct fwtty_port *tmp = peer->port;

                        fwserial_virt_plug_complete(peer, plug_req);
                        spin_unlock_bh(&peer->lock);

                        fwtty_write_port_status(tmp);
                        spin_lock_bh(&peer->lock);
                } else {
                        fwtty_err(&peer->unit, "PLUG_RSP error (%d)\n", rcode);
                        port = peer_revert_state(peer);
                }
        }
cleanup:
        spin_unlock_bh(&peer->lock);
        if (port)
                fwserial_release_port(port, false);
        kfree(pkt);
}

static void fwserial_handle_unplug_req(struct work_struct *work)
{
        struct fwtty_peer *peer = to_peer(work, work);
        struct fwtty_port *port = NULL;
        struct fwserial_mgmt_pkt *pkt;
        int rcode;

        pkt = kmalloc(sizeof(*pkt), GFP_KERNEL);
        if (!pkt)
                return;

        spin_lock_bh(&peer->lock);

        switch (peer->state) {
        case FWPS_ATTACHED:
                fill_unplug_rsp_ok(pkt);
                peer_set_state(peer, FWPS_UNPLUG_RESPONDING);
                break;

        case FWPS_UNPLUG_PENDING:
                if (peer->serial->card->guid > peer->guid)
                        goto cleanup;

                /* We lost - send unplug rsp */
                del_timer(&peer->timer);
                fill_unplug_rsp_ok(pkt);
                peer_set_state(peer, FWPS_UNPLUG_RESPONDING);
                break;

        default:
                fill_unplug_rsp_nack(pkt);
        }

        spin_unlock_bh(&peer->lock);

        rcode = fwserial_send_mgmt_sync(peer, pkt);

        spin_lock_bh(&peer->lock);
        if (peer->state == FWPS_UNPLUG_RESPONDING) {
                if (rcode != RCODE_COMPLETE)
                        fwtty_err(&peer->unit, "UNPLUG_RSP error (%d)\n",
                                  rcode);
                port = peer_revert_state(peer);
        }
cleanup:
        spin_unlock_bh(&peer->lock);
        if (port)
                fwserial_release_port(port, true);
        kfree(pkt);
}

static int fwserial_parse_mgmt_write(struct fwtty_peer *peer,
                                     struct fwserial_mgmt_pkt *pkt,
                                     unsigned long long addr,
                                     size_t len)
{
        struct fwtty_port *port = NULL;
        bool reset = false;
        int rcode;

        if (addr != fwserial_mgmt_addr_handler.offset || len < sizeof(pkt->hdr))
                return RCODE_ADDRESS_ERROR;

        if (len != be16_to_cpu(pkt->hdr.len) ||
            len != mgmt_pkt_expected_len(pkt->hdr.code))
                return RCODE_DATA_ERROR;

        spin_lock_bh(&peer->lock);
        if (peer->state == FWPS_GONE) {
                /*
                 * This should never happen - it would mean that the
                 * remote unit that just wrote this transaction was
                 * already removed from the bus -- and the removal was
                 * processed before we rec'd this transaction
                 */
                fwtty_err(&peer->unit, "peer already removed\n");
                spin_unlock_bh(&peer->lock);
                return RCODE_ADDRESS_ERROR;
        }

        rcode = RCODE_COMPLETE;

        fwtty_dbg(&peer->unit, "mgmt: hdr.code: %04hx\n", pkt->hdr.code);

        switch (be16_to_cpu(pkt->hdr.code) & FWSC_CODE_MASK) {
        case FWSC_VIRT_CABLE_PLUG:
                if (work_pending(&peer->work)) {
                        fwtty_err(&peer->unit, "plug req: busy\n");
                        rcode = RCODE_CONFLICT_ERROR;

                } else {
                        peer->work_params.plug_req = pkt->plug_req;
                        peer->workfn = fwserial_handle_plug_req;
                        queue_work(system_unbound_wq, &peer->work);
                }
                break;

        case FWSC_VIRT_CABLE_PLUG_RSP:
                if (peer->state != FWPS_PLUG_PENDING) {
                        rcode = RCODE_CONFLICT_ERROR;

                } else if (be16_to_cpu(pkt->hdr.code) & FWSC_RSP_NACK) {
                        fwtty_notice(&peer->unit, "NACK plug rsp\n");
                        port = peer_revert_state(peer);

                } else {
                        struct fwtty_port *tmp = peer->port;

                        fwserial_virt_plug_complete(peer, &pkt->plug_rsp);
                        spin_unlock_bh(&peer->lock);

                        fwtty_write_port_status(tmp);
                        spin_lock_bh(&peer->lock);
                }
                break;

        case FWSC_VIRT_CABLE_UNPLUG:
                if (work_pending(&peer->work)) {
                        fwtty_err(&peer->unit, "unplug req: busy\n");
                        rcode = RCODE_CONFLICT_ERROR;
                } else {
                        peer->workfn = fwserial_handle_unplug_req;
                        queue_work(system_unbound_wq, &peer->work);
                }
                break;

        case FWSC_VIRT_CABLE_UNPLUG_RSP:
                if (peer->state != FWPS_UNPLUG_PENDING) {
                        rcode = RCODE_CONFLICT_ERROR;
                } else {
                        if (be16_to_cpu(pkt->hdr.code) & FWSC_RSP_NACK)
                                fwtty_notice(&peer->unit, "NACK unplug?\n");
                        port = peer_revert_state(peer);
                        reset = true;
                }
                break;

        default:
                fwtty_err(&peer->unit, "unknown mgmt code %d\n",
                          be16_to_cpu(pkt->hdr.code));
                rcode = RCODE_DATA_ERROR;
        }
        spin_unlock_bh(&peer->lock);

        if (port)
                fwserial_release_port(port, reset);

        return rcode;
}

/**
 * fwserial_mgmt_handler: bus address handler for mgmt requests
 * @parameters: fw_address_callback_t as specified by firewire core interface
 *
 * This handler is responsible for handling virtual cable requests from remotes
 * for all cards.
 */
static void fwserial_mgmt_handler(struct fw_card *card,
                                  struct fw_request *request,
                                  int tcode, int destination, int source,
                                  int generation,
                                  unsigned long long addr,
                                  void *data, size_t len,
                                  void *callback_data)
{
        struct fwserial_mgmt_pkt *pkt = data;
        struct fwtty_peer *peer;
        int rcode;

        rcu_read_lock();
        peer = __fwserial_peer_by_node_id(card, generation, source);
        if (!peer) {
                fwtty_dbg(card, "peer(%d:%x) not found\n", generation, source);
                __dump_peer_list(card);
                rcode = RCODE_CONFLICT_ERROR;

        } else {
                switch (tcode) {
                case TCODE_WRITE_BLOCK_REQUEST:
                        rcode = fwserial_parse_mgmt_write(peer, pkt, addr, len);
                        break;

                default:
                        rcode = RCODE_TYPE_ERROR;
                }
        }

        rcu_read_unlock();
        fw_send_response(card, request, rcode);
}

static int __init fwserial_init(void)
{
        int err, num_loops = !!(create_loop_dev);

        /* XXX: placeholder for a "firewire" debugfs node */
        fwserial_debugfs = debugfs_create_dir(KBUILD_MODNAME, NULL);

        /* num_ttys/num_ports must not be set above the static alloc avail */
        if (num_ttys + num_loops > MAX_CARD_PORTS)
                num_ttys = MAX_CARD_PORTS - num_loops;

        num_ports = num_ttys + num_loops;

        fwtty_driver = tty_alloc_driver(MAX_TOTAL_PORTS, TTY_DRIVER_REAL_RAW
                                        | TTY_DRIVER_DYNAMIC_DEV);
        if (IS_ERR(fwtty_driver)) {
                err = PTR_ERR(fwtty_driver);
                goto remove_debugfs;
        }

        fwtty_driver->driver_name       = KBUILD_MODNAME;
        fwtty_driver->name              = tty_dev_name;
        fwtty_driver->major             = 0;
        fwtty_driver->minor_start       = 0;
        fwtty_driver->type              = TTY_DRIVER_TYPE_SERIAL;
        fwtty_driver->subtype           = SERIAL_TYPE_NORMAL;
        fwtty_driver->init_termios          = tty_std_termios;
        fwtty_driver->init_termios.c_cflag  |= CLOCAL;
        tty_set_operations(fwtty_driver, &fwtty_ops);

        err = tty_register_driver(fwtty_driver);
        if (err) {
                pr_err("register tty driver failed (%d)\n", err);
                goto put_tty;
        }

        if (create_loop_dev) {
                fwloop_driver = tty_alloc_driver(MAX_TOTAL_PORTS / num_ports,
                                                 TTY_DRIVER_REAL_RAW
                                                 | TTY_DRIVER_DYNAMIC_DEV);
                if (IS_ERR(fwloop_driver)) {
                        err = PTR_ERR(fwloop_driver);
                        goto unregister_driver;
                }

                fwloop_driver->driver_name      = KBUILD_MODNAME "_loop";
                fwloop_driver->name             = loop_dev_name;
                fwloop_driver->major            = 0;
                fwloop_driver->minor_start      = 0;
                fwloop_driver->type             = TTY_DRIVER_TYPE_SERIAL;
                fwloop_driver->subtype          = SERIAL_TYPE_NORMAL;
                fwloop_driver->init_termios         = tty_std_termios;
                fwloop_driver->init_termios.c_cflag  |= CLOCAL;
                tty_set_operations(fwloop_driver, &fwloop_ops);

                err = tty_register_driver(fwloop_driver);
                if (err) {
                        pr_err("register loop driver failed (%d)\n", err);
                        goto put_loop;
                }
        }

        fwtty_txn_cache = kmem_cache_create("fwtty_txn_cache",
                                            sizeof(struct fwtty_transaction),
                                            0, 0, NULL);
        if (!fwtty_txn_cache) {
                err = -ENOMEM;
                goto unregister_loop;
        }

        /*
         * Ideally, this address handler would be registered per local node
         * (rather than the same handler for all local nodes). However,
         * since the firewire core requires the config rom descriptor *before*
         * the local unit device(s) are created, a single management handler
         * must suffice for all local serial units.
         */
        fwserial_mgmt_addr_handler.length = sizeof(struct fwserial_mgmt_pkt);
        fwserial_mgmt_addr_handler.address_callback = fwserial_mgmt_handler;

        err = fw_core_add_address_handler(&fwserial_mgmt_addr_handler,
                                          &fwserial_mgmt_addr_region);
        if (err) {
                pr_err("add management handler failed (%d)\n", err);
                goto destroy_cache;
        }

        fwserial_unit_directory_data.unit_addr_offset =
                FW_UNIT_ADDRESS(fwserial_mgmt_addr_handler.offset);
        err = fw_core_add_descriptor(&fwserial_unit_directory);
        if (err) {
                pr_err("add unit descriptor failed (%d)\n", err);
                goto remove_handler;
        }

        err = driver_register(&fwserial_driver.driver);
        if (err) {
                pr_err("register fwserial driver failed (%d)\n", err);
                goto remove_descriptor;
        }

        return 0;

remove_descriptor:
        fw_core_remove_descriptor(&fwserial_unit_directory);
remove_handler:
        fw_core_remove_address_handler(&fwserial_mgmt_addr_handler);
destroy_cache:
        kmem_cache_destroy(fwtty_txn_cache);
unregister_loop:
        if (create_loop_dev)
                tty_unregister_driver(fwloop_driver);
put_loop:
        if (create_loop_dev)
                put_tty_driver(fwloop_driver);
unregister_driver:
        tty_unregister_driver(fwtty_driver);
put_tty:
        put_tty_driver(fwtty_driver);
remove_debugfs:
        debugfs_remove_recursive(fwserial_debugfs);

        return err;
}

static void __exit fwserial_exit(void)
{
        driver_unregister(&fwserial_driver.driver);
        fw_core_remove_descriptor(&fwserial_unit_directory);
        fw_core_remove_address_handler(&fwserial_mgmt_addr_handler);
        kmem_cache_destroy(fwtty_txn_cache);
        if (create_loop_dev) {
                tty_unregister_driver(fwloop_driver);
                put_tty_driver(fwloop_driver);
        }
        tty_unregister_driver(fwtty_driver);
        put_tty_driver(fwtty_driver);
        debugfs_remove_recursive(fwserial_debugfs);
}

module_init(fwserial_init);
module_exit(fwserial_exit);

MODULE_AUTHOR("Peter Hurley (peter@hurleysoftware.com)");
MODULE_DESCRIPTION("FireWire Serial TTY Driver");
MODULE_LICENSE("GPL");
MODULE_DEVICE_TABLE(ieee1394, fwserial_id_table);
MODULE_PARM_DESC(ttys, "Number of ttys to create for each local firewire node");
MODULE_PARM_DESC(auto, "Auto-connect a tty to each firewire node discovered");
MODULE_PARM_DESC(loop, "Create a loopback device, fwloop<n>, with ttys");