// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (C) 2004 Hollis Blanchard <hollisb@us.ibm.com>, IBM
 */

/* Host Virtual Serial Interface (HVSI) is a protocol between the hosted OS
 * and the service processor on IBM pSeries servers. On these servers, there
 * are no serial ports under the OS's control, and sometimes there is no other
 * console available either. However, the service processor has two standard
 * serial ports, so this over-complicated protocol allows the OS to control
 * those ports by proxy.
 *
 * Besides data, the procotol supports the reading/writing of the serial
 * port's DTR line, and the reading of the CD line. This is to allow the OS to
 * control a modem attached to the service processor's serial port. Note that
 * the OS cannot change the speed of the port through this protocol.
 */

#undef DEBUG

#include <linux/console.h>
#include <linux/ctype.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/major.h>
#include <linux/kernel.h>
#include <linux/spinlock.h>
#include <linux/sysrq.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <asm/hvcall.h>
#include <asm/hvconsole.h>
#include <asm/prom.h>
#include <linux/uaccess.h>
#include <asm/vio.h>
#include <asm/param.h>
#include <asm/hvsi.h>

#define HVSI_MAJOR      229
#define HVSI_MINOR      128
#define MAX_NR_HVSI_CONSOLES 4

#define HVSI_TIMEOUT (5*HZ)
#define HVSI_VERSION 1
#define HVSI_MAX_PACKET 256
#define HVSI_MAX_READ 16
#define HVSI_MAX_OUTGOING_DATA 12
#define N_OUTBUF 12

/*
 * we pass data via two 8-byte registers, so we would like our char arrays
 * properly aligned for those loads.
 */
#define __ALIGNED__     __attribute__((__aligned__(sizeof(long))))

struct hvsi_struct {
        struct tty_port port;
        struct delayed_work writer;
        struct work_struct handshaker;
        wait_queue_head_t emptyq; /* woken when outbuf is emptied */
        wait_queue_head_t stateq; /* woken when HVSI state changes */
        spinlock_t lock;
        int index;
        uint8_t throttle_buf[128];
        uint8_t outbuf[N_OUTBUF]; /* to implement write_room and chars_in_buffer */
        /* inbuf is for packet reassembly. leave a little room for leftovers. */
        uint8_t inbuf[HVSI_MAX_PACKET + HVSI_MAX_READ];
        uint8_t *inbuf_end;
        int n_throttle;
        int n_outbuf;
        uint32_t vtermno;
        uint32_t virq;
        atomic_t seqno; /* HVSI packet sequence number */
        uint16_t mctrl;
        uint8_t state;  /* HVSI protocol state */
        uint8_t flags;
#ifdef CONFIG_MAGIC_SYSRQ
        uint8_t sysrq;
#endif /* CONFIG_MAGIC_SYSRQ */
};
static struct hvsi_struct hvsi_ports[MAX_NR_HVSI_CONSOLES];

static struct tty_driver *hvsi_driver;
static int hvsi_count;
static int (*hvsi_wait)(struct hvsi_struct *hp, int state);

enum HVSI_PROTOCOL_STATE {
        HVSI_CLOSED,
        HVSI_WAIT_FOR_VER_RESPONSE,
        HVSI_WAIT_FOR_VER_QUERY,
        HVSI_OPEN,
        HVSI_WAIT_FOR_MCTRL_RESPONSE,
        HVSI_FSP_DIED,
};
#define HVSI_CONSOLE 0x1

static inline int is_console(struct hvsi_struct *hp)
{
        return hp->flags & HVSI_CONSOLE;
}

static inline int is_open(struct hvsi_struct *hp)
{
        /* if we're waiting for an mctrl then we're already open */
        return (hp->state == HVSI_OPEN)
                        || (hp->state == HVSI_WAIT_FOR_MCTRL_RESPONSE);
}

static inline void print_state(struct hvsi_struct *hp)
{
#ifdef DEBUG
        static const char *state_names[] = {
                "HVSI_CLOSED",
                "HVSI_WAIT_FOR_VER_RESPONSE",
                "HVSI_WAIT_FOR_VER_QUERY",
                "HVSI_OPEN",
                "HVSI_WAIT_FOR_MCTRL_RESPONSE",
                "HVSI_FSP_DIED",
        };
        const char *name = (hp->state < ARRAY_SIZE(state_names))
                ? state_names[hp->state] : "UNKNOWN";

        pr_debug("hvsi%i: state = %s\n", hp->index, name);
#endif /* DEBUG */
}

static inline void __set_state(struct hvsi_struct *hp, int state)
{
        hp->state = state;
        print_state(hp);
        wake_up_all(&hp->stateq);
}

static inline void set_state(struct hvsi_struct *hp, int state)
{
        unsigned long flags;

        spin_lock_irqsave(&hp->lock, flags);
        __set_state(hp, state);
        spin_unlock_irqrestore(&hp->lock, flags);
}

static inline int len_packet(const uint8_t *packet)
{
        return (int)((struct hvsi_header *)packet)->len;
}

static inline int is_header(const uint8_t *packet)
{
        struct hvsi_header *header = (struct hvsi_header *)packet;
        return header->type >= VS_QUERY_RESPONSE_PACKET_HEADER;
}

static inline int got_packet(const struct hvsi_struct *hp, uint8_t *packet)
{
        if (hp->inbuf_end < packet + sizeof(struct hvsi_header))
                return 0; /* don't even have the packet header */

        if (hp->inbuf_end < (packet + len_packet(packet)))
                return 0; /* don't have the rest of the packet */

        return 1;
}

/* shift remaining bytes in packetbuf down */
static void compact_inbuf(struct hvsi_struct *hp, uint8_t *read_to)
{
        int remaining = (int)(hp->inbuf_end - read_to);

        pr_debug("%s: %i chars remain\n", __func__, remaining);

        if (read_to != hp->inbuf)
                memmove(hp->inbuf, read_to, remaining);

        hp->inbuf_end = hp->inbuf + remaining;
}

#ifdef DEBUG
#define dbg_dump_packet(packet) dump_packet(packet)
#define dbg_dump_hex(data, len) dump_hex(data, len)
#else
#define dbg_dump_packet(packet) do { } while (0)
#define dbg_dump_hex(data, len) do { } while (0)
#endif

static void dump_hex(const uint8_t *data, int len)
{
        int i;

        printk("    ");
        for (i=0; i < len; i++)
                printk("%.2x", data[i]);

        printk("\n    ");
        for (i=0; i < len; i++) {
                if (isprint(data[i]))
                        printk("%c", data[i]);
                else
                        printk(".");
        }
        printk("\n");
}

static void dump_packet(uint8_t *packet)
{
        struct hvsi_header *header = (struct hvsi_header *)packet;

        printk("type 0x%x, len %i, seqno %i:\n", header->type, header->len,
                        header->seqno);

        dump_hex(packet, header->len);
}

static int hvsi_read(struct hvsi_struct *hp, char *buf, int count)
{
        unsigned long got;

        got = hvc_get_chars(hp->vtermno, buf, count);

        return got;
}

static void hvsi_recv_control(struct hvsi_struct *hp, uint8_t *packet,
        struct tty_struct *tty, struct hvsi_struct **to_handshake)
{
        struct hvsi_control *header = (struct hvsi_control *)packet;

        switch (be16_to_cpu(header->verb)) {
                case VSV_MODEM_CTL_UPDATE:
                        if ((be32_to_cpu(header->word) & HVSI_TSCD) == 0) {
                                /* CD went away; no more connection */
                                pr_debug("hvsi%i: CD dropped\n", hp->index);
                                hp->mctrl &= TIOCM_CD;
                                if (tty && !C_CLOCAL(tty))
                                        tty_hangup(tty);
                        }
                        break;
                case VSV_CLOSE_PROTOCOL:
                        pr_debug("hvsi%i: service processor came back\n", hp->index);
                        if (hp->state != HVSI_CLOSED) {
                                *to_handshake = hp;
                        }
                        break;
                default:
                        printk(KERN_WARNING "hvsi%i: unknown HVSI control packet: ",
                                hp->index);
                        dump_packet(packet);
                        break;
        }
}

static void hvsi_recv_response(struct hvsi_struct *hp, uint8_t *packet)
{
        struct hvsi_query_response *resp = (struct hvsi_query_response *)packet;
        uint32_t mctrl_word;

        switch (hp->state) {
                case HVSI_WAIT_FOR_VER_RESPONSE:
                        __set_state(hp, HVSI_WAIT_FOR_VER_QUERY);
                        break;
                case HVSI_WAIT_FOR_MCTRL_RESPONSE:
                        hp->mctrl = 0;
                        mctrl_word = be32_to_cpu(resp->u.mctrl_word);
                        if (mctrl_word & HVSI_TSDTR)
                                hp->mctrl |= TIOCM_DTR;
                        if (mctrl_word & HVSI_TSCD)
                                hp->mctrl |= TIOCM_CD;
                        __set_state(hp, HVSI_OPEN);
                        break;
                default:
                        printk(KERN_ERR "hvsi%i: unexpected query response: ", hp->index);
                        dump_packet(packet);
                        break;
        }
}

/* respond to service processor's version query */
static int hvsi_version_respond(struct hvsi_struct *hp, uint16_t query_seqno)
{
        struct hvsi_query_response packet __ALIGNED__;
        int wrote;

        packet.hdr.type = VS_QUERY_RESPONSE_PACKET_HEADER;
        packet.hdr.len = sizeof(struct hvsi_query_response);
        packet.hdr.seqno = cpu_to_be16(atomic_inc_return(&hp->seqno));
        packet.verb = cpu_to_be16(VSV_SEND_VERSION_NUMBER);
        packet.u.version = HVSI_VERSION;
        packet.query_seqno = cpu_to_be16(query_seqno+1);

        pr_debug("%s: sending %i bytes\n", __func__, packet.hdr.len);
        dbg_dump_hex((uint8_t*)&packet, packet.hdr.len);

        wrote = hvc_put_chars(hp->vtermno, (char *)&packet, packet.hdr.len);
        if (wrote != packet.hdr.len) {
                printk(KERN_ERR "hvsi%i: couldn't send query response!\n",
                        hp->index);
                return -EIO;
        }

        return 0;
}

static void hvsi_recv_query(struct hvsi_struct *hp, uint8_t *packet)
{
        struct hvsi_query *query = (struct hvsi_query *)packet;

        switch (hp->state) {
                case HVSI_WAIT_FOR_VER_QUERY:
                        hvsi_version_respond(hp, be16_to_cpu(query->hdr.seqno));
                        __set_state(hp, HVSI_OPEN);
                        break;
                default:
                        printk(KERN_ERR "hvsi%i: unexpected query: ", hp->index);
                        dump_packet(packet);
                        break;
        }
}

static void hvsi_insert_chars(struct hvsi_struct *hp, const char *buf, int len)
{
        int i;

        for (i=0; i < len; i++) {
                char c = buf[i];
#ifdef CONFIG_MAGIC_SYSRQ
                if (c == '\0') {
                        hp->sysrq = 1;
                        continue;
                } else if (hp->sysrq) {
                        handle_sysrq(c);
                        hp->sysrq = 0;
                        continue;
                }
#endif /* CONFIG_MAGIC_SYSRQ */
                tty_insert_flip_char(&hp->port, c, 0);
        }
}

/*
 * We could get 252 bytes of data at once here. But the tty layer only
 * throttles us at TTY_THRESHOLD_THROTTLE (128) bytes, so we could overflow
 * it. Accordingly we won't send more than 128 bytes at a time to the flip
 * buffer, which will give the tty buffer a chance to throttle us. Should the
 * value of TTY_THRESHOLD_THROTTLE change in n_tty.c, this code should be
 * revisited.
 */
#define TTY_THRESHOLD_THROTTLE 128
static bool hvsi_recv_data(struct hvsi_struct *hp, const uint8_t *packet)
{
        const struct hvsi_header *header = (const struct hvsi_header *)packet;
        const uint8_t *data = packet + sizeof(struct hvsi_header);
        int datalen = header->len - sizeof(struct hvsi_header);
        int overflow = datalen - TTY_THRESHOLD_THROTTLE;

        pr_debug("queueing %i chars '%.*s'\n", datalen, datalen, data);

        if (datalen == 0)
                return false;

        if (overflow > 0) {
                pr_debug("%s: got >TTY_THRESHOLD_THROTTLE bytes\n", __func__);
                datalen = TTY_THRESHOLD_THROTTLE;
        }

        hvsi_insert_chars(hp, data, datalen);

        if (overflow > 0) {
                /*
                 * we still have more data to deliver, so we need to save off the
                 * overflow and send it later
                 */
                pr_debug("%s: deferring overflow\n", __func__);
                memcpy(hp->throttle_buf, data + TTY_THRESHOLD_THROTTLE, overflow);
                hp->n_throttle = overflow;
        }

        return true;
}

/*
 * Returns true/false indicating data successfully read from hypervisor.
 * Used both to get packets for tty connections and to advance the state
 * machine during console handshaking (in which case tty = NULL and we ignore
 * incoming data).
 */
static int hvsi_load_chunk(struct hvsi_struct *hp, struct tty_struct *tty,
                struct hvsi_struct **handshake)
{
        uint8_t *packet = hp->inbuf;
        int chunklen;
        bool flip = false;

        *handshake = NULL;

        chunklen = hvsi_read(hp, hp->inbuf_end, HVSI_MAX_READ);
        if (chunklen == 0) {
                pr_debug("%s: 0-length read\n", __func__);
                return 0;
        }

        pr_debug("%s: got %i bytes\n", __func__, chunklen);
        dbg_dump_hex(hp->inbuf_end, chunklen);

        hp->inbuf_end += chunklen;

        /* handle all completed packets */
        while ((packet < hp->inbuf_end) && got_packet(hp, packet)) {
                struct hvsi_header *header = (struct hvsi_header *)packet;

                if (!is_header(packet)) {
                        printk(KERN_ERR "hvsi%i: got malformed packet\n", hp->index);
                        /* skip bytes until we find a header or run out of data */
                        while ((packet < hp->inbuf_end) && (!is_header(packet)))
                                packet++;
                        continue;
                }

                pr_debug("%s: handling %i-byte packet\n", __func__,
                                len_packet(packet));
                dbg_dump_packet(packet);

                switch (header->type) {
                        case VS_DATA_PACKET_HEADER:
                                if (!is_open(hp))
                                        break;
                                flip = hvsi_recv_data(hp, packet);
                                break;
                        case VS_CONTROL_PACKET_HEADER:
                                hvsi_recv_control(hp, packet, tty, handshake);
                                break;
                        case VS_QUERY_RESPONSE_PACKET_HEADER:
                                hvsi_recv_response(hp, packet);
                                break;
                        case VS_QUERY_PACKET_HEADER:
                                hvsi_recv_query(hp, packet);
                                break;
                        default:
                                printk(KERN_ERR "hvsi%i: unknown HVSI packet type 0x%x\n",
                                                hp->index, header->type);
                                dump_packet(packet);
                                break;
                }

                packet += len_packet(packet);

                if (*handshake) {
                        pr_debug("%s: handshake\n", __func__);
                        break;
                }
        }

        compact_inbuf(hp, packet);

        if (flip)
                tty_flip_buffer_push(&hp->port);

        return 1;
}

static void hvsi_send_overflow(struct hvsi_struct *hp)
{
        pr_debug("%s: delivering %i bytes overflow\n", __func__,
                        hp->n_throttle);

        hvsi_insert_chars(hp, hp->throttle_buf, hp->n_throttle);
        hp->n_throttle = 0;
}

/*
 * must get all pending data because we only get an irq on empty->non-empty
 * transition
 */
static irqreturn_t hvsi_interrupt(int irq, void *arg)
{
        struct hvsi_struct *hp = (struct hvsi_struct *)arg;
        struct hvsi_struct *handshake;
        struct tty_struct *tty;
        unsigned long flags;
        int again = 1;

        pr_debug("%s\n", __func__);

        tty = tty_port_tty_get(&hp->port);

        while (again) {
                spin_lock_irqsave(&hp->lock, flags);
                again = hvsi_load_chunk(hp, tty, &handshake);
                spin_unlock_irqrestore(&hp->lock, flags);

                if (handshake) {
                        pr_debug("hvsi%i: attempting re-handshake\n", handshake->index);
                        schedule_work(&handshake->handshaker);
                }
        }

        spin_lock_irqsave(&hp->lock, flags);
        if (tty && hp->n_throttle && !tty_throttled(tty)) {
                /* we weren't hung up and we weren't throttled, so we can
                 * deliver the rest now */
                hvsi_send_overflow(hp);
                tty_flip_buffer_push(&hp->port);
        }
        spin_unlock_irqrestore(&hp->lock, flags);

        tty_kref_put(tty);

        return IRQ_HANDLED;
}

/* for boot console, before the irq handler is running */
static int __init poll_for_state(struct hvsi_struct *hp, int state)
{
        unsigned long end_jiffies = jiffies + HVSI_TIMEOUT;

        for (;;) {
                hvsi_interrupt(hp->virq, (void *)hp); /* get pending data */

                if (hp->state == state)
                        return 0;

                mdelay(5);
                if (time_after(jiffies, end_jiffies))
                        return -EIO;
        }
}

/* wait for irq handler to change our state */
static int wait_for_state(struct hvsi_struct *hp, int state)
{
        int ret = 0;

        if (!wait_event_timeout(hp->stateq, (hp->state == state), HVSI_TIMEOUT))
                ret = -EIO;

        return ret;
}

static int hvsi_query(struct hvsi_struct *hp, uint16_t verb)
{
        struct hvsi_query packet __ALIGNED__;
        int wrote;

        packet.hdr.type = VS_QUERY_PACKET_HEADER;
        packet.hdr.len = sizeof(struct hvsi_query);
        packet.hdr.seqno = cpu_to_be16(atomic_inc_return(&hp->seqno));
        packet.verb = cpu_to_be16(verb);

        pr_debug("%s: sending %i bytes\n", __func__, packet.hdr.len);
        dbg_dump_hex((uint8_t*)&packet, packet.hdr.len);

        wrote = hvc_put_chars(hp->vtermno, (char *)&packet, packet.hdr.len);
        if (wrote != packet.hdr.len) {
                printk(KERN_ERR "hvsi%i: couldn't send query (%i)!\n", hp->index,
                        wrote);
                return -EIO;
        }

        return 0;
}

static int hvsi_get_mctrl(struct hvsi_struct *hp)
{
        int ret;

        set_state(hp, HVSI_WAIT_FOR_MCTRL_RESPONSE);
        hvsi_query(hp, VSV_SEND_MODEM_CTL_STATUS);

        ret = hvsi_wait(hp, HVSI_OPEN);
        if (ret < 0) {
                printk(KERN_ERR "hvsi%i: didn't get modem flags\n", hp->index);
                set_state(hp, HVSI_OPEN);
                return ret;
        }

        pr_debug("%s: mctrl 0x%x\n", __func__, hp->mctrl);

        return 0;
}

/* note that we can only set DTR */
static int hvsi_set_mctrl(struct hvsi_struct *hp, uint16_t mctrl)
{
        struct hvsi_control packet __ALIGNED__;
        int wrote;

        packet.hdr.type = VS_CONTROL_PACKET_HEADER;
        packet.hdr.seqno = cpu_to_be16(atomic_inc_return(&hp->seqno));
        packet.hdr.len = sizeof(struct hvsi_control);
        packet.verb = cpu_to_be16(VSV_SET_MODEM_CTL);
        packet.mask = cpu_to_be32(HVSI_TSDTR);

        if (mctrl & TIOCM_DTR)
                packet.word = cpu_to_be32(HVSI_TSDTR);

        pr_debug("%s: sending %i bytes\n", __func__, packet.hdr.len);
        dbg_dump_hex((uint8_t*)&packet, packet.hdr.len);

        wrote = hvc_put_chars(hp->vtermno, (char *)&packet, packet.hdr.len);
        if (wrote != packet.hdr.len) {
                printk(KERN_ERR "hvsi%i: couldn't set DTR!\n", hp->index);
                return -EIO;
        }

        return 0;
}

static void hvsi_drain_input(struct hvsi_struct *hp)
{
        uint8_t buf[HVSI_MAX_READ] __ALIGNED__;
        unsigned long end_jiffies = jiffies + HVSI_TIMEOUT;

        while (time_before(end_jiffies, jiffies))
                if (0 == hvsi_read(hp, buf, HVSI_MAX_READ))
                        break;
}

static int hvsi_handshake(struct hvsi_struct *hp)
{
        int ret;

        /*
         * We could have a CLOSE or other data waiting for us before we even try
         * to open; try to throw it all away so we don't get confused. (CLOSE
         * is the first message sent up the pipe when the FSP comes online. We
         * need to distinguish between "it came up a while ago and we're the first
         * user" and "it was just reset before it saw our handshake packet".)
         */
        hvsi_drain_input(hp);

        set_state(hp, HVSI_WAIT_FOR_VER_RESPONSE);
        ret = hvsi_query(hp, VSV_SEND_VERSION_NUMBER);
        if (ret < 0) {
                printk(KERN_ERR "hvsi%i: couldn't send version query\n", hp->index);
                return ret;
        }

        ret = hvsi_wait(hp, HVSI_OPEN);
        if (ret < 0)
                return ret;

        return 0;
}

static void hvsi_handshaker(struct work_struct *work)
{
        struct hvsi_struct *hp =
                container_of(work, struct hvsi_struct, handshaker);

        if (hvsi_handshake(hp) >= 0)
                return;

        printk(KERN_ERR "hvsi%i: re-handshaking failed\n", hp->index);
        if (is_console(hp)) {
                /*
                 * ttys will re-attempt the handshake via hvsi_open, but
                 * the console will not.
                 */
                printk(KERN_ERR "hvsi%i: lost console!\n", hp->index);
        }
}

static int hvsi_put_chars(struct hvsi_struct *hp, const char *buf, int count)
{
        struct hvsi_data packet __ALIGNED__;
        int ret;

        BUG_ON(count > HVSI_MAX_OUTGOING_DATA);

        packet.hdr.type = VS_DATA_PACKET_HEADER;
        packet.hdr.seqno = cpu_to_be16(atomic_inc_return(&hp->seqno));
        packet.hdr.len = count + sizeof(struct hvsi_header);
        memcpy(&packet.data, buf, count);

        ret = hvc_put_chars(hp->vtermno, (char *)&packet, packet.hdr.len);
        if (ret == packet.hdr.len) {
                /* return the number of chars written, not the packet length */
                return count;
        }
        return ret; /* return any errors */
}

static void hvsi_close_protocol(struct hvsi_struct *hp)
{
        struct hvsi_control packet __ALIGNED__;

        packet.hdr.type = VS_CONTROL_PACKET_HEADER;
        packet.hdr.seqno = cpu_to_be16(atomic_inc_return(&hp->seqno));
        packet.hdr.len = 6;
        packet.verb = cpu_to_be16(VSV_CLOSE_PROTOCOL);

        pr_debug("%s: sending %i bytes\n", __func__, packet.hdr.len);
        dbg_dump_hex((uint8_t*)&packet, packet.hdr.len);

        hvc_put_chars(hp->vtermno, (char *)&packet, packet.hdr.len);
}

static int hvsi_open(struct tty_struct *tty, struct file *filp)
{
        struct hvsi_struct *hp;
        unsigned long flags;
        int ret;

        pr_debug("%s\n", __func__);

        hp = &hvsi_ports[tty->index];

        tty->driver_data = hp;

        mb();
        if (hp->state == HVSI_FSP_DIED)
                return -EIO;

        tty_port_tty_set(&hp->port, tty);
        spin_lock_irqsave(&hp->lock, flags);
        hp->port.count++;
        atomic_set(&hp->seqno, 0);
        h_vio_signal(hp->vtermno, VIO_IRQ_ENABLE);
        spin_unlock_irqrestore(&hp->lock, flags);

        if (is_console(hp))
                return 0; /* this has already been handshaked as the console */

        ret = hvsi_handshake(hp);
        if (ret < 0) {
                printk(KERN_ERR "%s: HVSI handshaking failed\n", tty->name);
                return ret;
        }

        ret = hvsi_get_mctrl(hp);
        if (ret < 0) {
                printk(KERN_ERR "%s: couldn't get initial modem flags\n", tty->name);
                return ret;
        }

        ret = hvsi_set_mctrl(hp, hp->mctrl | TIOCM_DTR);
        if (ret < 0) {
                printk(KERN_ERR "%s: couldn't set DTR\n", tty->name);
                return ret;
        }

        return 0;
}

/* wait for hvsi_write_worker to empty hp->outbuf */
static void hvsi_flush_output(struct hvsi_struct *hp)
{
        wait_event_timeout(hp->emptyq, (hp->n_outbuf <= 0), HVSI_TIMEOUT);

        /* 'writer' could still be pending if it didn't see n_outbuf = 0 yet */
        cancel_delayed_work_sync(&hp->writer);
        flush_work(&hp->handshaker);

        /*
         * it's also possible that our timeout expired and hvsi_write_worker
         * didn't manage to push outbuf. poof.
         */
        hp->n_outbuf = 0;
}

static void hvsi_close(struct tty_struct *tty, struct file *filp)
{
        struct hvsi_struct *hp = tty->driver_data;
        unsigned long flags;

        pr_debug("%s\n", __func__);

        if (tty_hung_up_p(filp))
                return;

        spin_lock_irqsave(&hp->lock, flags);

        if (--hp->port.count == 0) {
                tty_port_tty_set(&hp->port, NULL);
                hp->inbuf_end = hp->inbuf; /* discard remaining partial packets */

                /* only close down connection if it is not the console */
                if (!is_console(hp)) {
                        h_vio_signal(hp->vtermno, VIO_IRQ_DISABLE); /* no more irqs */
                        __set_state(hp, HVSI_CLOSED);
                        /*
                         * any data delivered to the tty layer after this will be
                         * discarded (except for XON/XOFF)
                         */
                        tty->closing = 1;

                        spin_unlock_irqrestore(&hp->lock, flags);

                        /* let any existing irq handlers finish. no more will start. */
                        synchronize_irq(hp->virq);

                        /* hvsi_write_worker will re-schedule until outbuf is empty. */
                        hvsi_flush_output(hp);

                        /* tell FSP to stop sending data */
                        hvsi_close_protocol(hp);

                        /*
                         * drain anything FSP is still in the middle of sending, and let
                         * hvsi_handshake drain the rest on the next open.
                         */
                        hvsi_drain_input(hp);

                        spin_lock_irqsave(&hp->lock, flags);
                }
        } else if (hp->port.count < 0)
                printk(KERN_ERR "hvsi_close %lu: oops, count is %d\n",
                       hp - hvsi_ports, hp->port.count);

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

static void hvsi_hangup(struct tty_struct *tty)
{
        struct hvsi_struct *hp = tty->driver_data;
        unsigned long flags;

        pr_debug("%s\n", __func__);

        tty_port_tty_set(&hp->port, NULL);

        spin_lock_irqsave(&hp->lock, flags);
        hp->port.count = 0;
        hp->n_outbuf = 0;
        spin_unlock_irqrestore(&hp->lock, flags);
}

/* called with hp->lock held */
static void hvsi_push(struct hvsi_struct *hp)
{
        int n;

        if (hp->n_outbuf <= 0)
                return;

        n = hvsi_put_chars(hp, hp->outbuf, hp->n_outbuf);
        if (n > 0) {
                /* success */
                pr_debug("%s: wrote %i chars\n", __func__, n);
                hp->n_outbuf = 0;
        } else if (n == -EIO) {
                __set_state(hp, HVSI_FSP_DIED);
                printk(KERN_ERR "hvsi%i: service processor died\n", hp->index);
        }
}

/* hvsi_write_worker will keep rescheduling itself until outbuf is empty */
static void hvsi_write_worker(struct work_struct *work)
{
        struct hvsi_struct *hp =
                container_of(work, struct hvsi_struct, writer.work);
        unsigned long flags;
#ifdef DEBUG
        static long start_j = 0;

        if (start_j == 0)
                start_j = jiffies;
#endif /* DEBUG */

        spin_lock_irqsave(&hp->lock, flags);

        pr_debug("%s: %i chars in buffer\n", __func__, hp->n_outbuf);

        if (!is_open(hp)) {
                /*
                 * We could have a non-open connection if the service processor died
                 * while we were busily scheduling ourselves. In that case, it could
                 * be minutes before the service processor comes back, so only try
                 * again once a second.
                 */
                schedule_delayed_work(&hp->writer, HZ);
                goto out;
        }

        hvsi_push(hp);
        if (hp->n_outbuf > 0)
                schedule_delayed_work(&hp->writer, 10);
        else {
#ifdef DEBUG
                pr_debug("%s: outbuf emptied after %li jiffies\n", __func__,
                                jiffies - start_j);
                start_j = 0;
#endif /* DEBUG */
                wake_up_all(&hp->emptyq);
                tty_port_tty_wakeup(&hp->port);
        }

out:
        spin_unlock_irqrestore(&hp->lock, flags);
}

static int hvsi_write_room(struct tty_struct *tty)
{
        struct hvsi_struct *hp = tty->driver_data;

        return N_OUTBUF - hp->n_outbuf;
}

static int hvsi_chars_in_buffer(struct tty_struct *tty)
{
        struct hvsi_struct *hp = tty->driver_data;

        return hp->n_outbuf;
}

static int hvsi_write(struct tty_struct *tty,
                     const unsigned char *buf, int count)
{
        struct hvsi_struct *hp = tty->driver_data;
        const char *source = buf;
        unsigned long flags;
        int total = 0;
        int origcount = count;

        spin_lock_irqsave(&hp->lock, flags);

        pr_debug("%s: %i chars in buffer\n", __func__, hp->n_outbuf);

        if (!is_open(hp)) {
                /* we're either closing or not yet open; don't accept data */
                pr_debug("%s: not open\n", __func__);
                goto out;
        }

        /*
         * when the hypervisor buffer (16K) fills, data will stay in hp->outbuf
         * and hvsi_write_worker will be scheduled. subsequent hvsi_write() calls
         * will see there is no room in outbuf and return.
         */
        while ((count > 0) && (hvsi_write_room(tty) > 0)) {
                int chunksize = min(count, hvsi_write_room(tty));

                BUG_ON(hp->n_outbuf < 0);
                memcpy(hp->outbuf + hp->n_outbuf, source, chunksize);
                hp->n_outbuf += chunksize;

                total += chunksize;
                source += chunksize;
                count -= chunksize;
                hvsi_push(hp);
        }

        if (hp->n_outbuf > 0) {
                /*
                 * we weren't able to write it all to the hypervisor.
                 * schedule another push attempt.
                 */
                schedule_delayed_work(&hp->writer, 10);
        }

out:
        spin_unlock_irqrestore(&hp->lock, flags);

        if (total != origcount)
                pr_debug("%s: wanted %i, only wrote %i\n", __func__, origcount,
                        total);

        return total;
}

/*
 * I have never seen throttle or unthrottle called, so this little throttle
 * buffering scheme may or may not work.
 */
static void hvsi_throttle(struct tty_struct *tty)
{
        struct hvsi_struct *hp = tty->driver_data;

        pr_debug("%s\n", __func__);

        h_vio_signal(hp->vtermno, VIO_IRQ_DISABLE);
}

static void hvsi_unthrottle(struct tty_struct *tty)
{
        struct hvsi_struct *hp = tty->driver_data;
        unsigned long flags;

        pr_debug("%s\n", __func__);

        spin_lock_irqsave(&hp->lock, flags);
        if (hp->n_throttle) {
                hvsi_send_overflow(hp);
                tty_flip_buffer_push(&hp->port);
        }
        spin_unlock_irqrestore(&hp->lock, flags);


        h_vio_signal(hp->vtermno, VIO_IRQ_ENABLE);
}

static int hvsi_tiocmget(struct tty_struct *tty)
{
        struct hvsi_struct *hp = tty->driver_data;

        hvsi_get_mctrl(hp);
        return hp->mctrl;
}

static int hvsi_tiocmset(struct tty_struct *tty,
                                unsigned int set, unsigned int clear)
{
        struct hvsi_struct *hp = tty->driver_data;
        unsigned long flags;
        uint16_t new_mctrl;

        /* we can only alter DTR */
        clear &= TIOCM_DTR;
        set &= TIOCM_DTR;

        spin_lock_irqsave(&hp->lock, flags);

        new_mctrl = (hp->mctrl & ~clear) | set;

        if (hp->mctrl != new_mctrl) {
                hvsi_set_mctrl(hp, new_mctrl);
                hp->mctrl = new_mctrl;
        }
        spin_unlock_irqrestore(&hp->lock, flags);

        return 0;
}


static const struct tty_operations hvsi_ops = {
        .open = hvsi_open,
        .close = hvsi_close,
        .write = hvsi_write,
        .hangup = hvsi_hangup,
        .write_room = hvsi_write_room,
        .chars_in_buffer = hvsi_chars_in_buffer,
        .throttle = hvsi_throttle,
        .unthrottle = hvsi_unthrottle,
        .tiocmget = hvsi_tiocmget,
        .tiocmset = hvsi_tiocmset,
};

static int __init hvsi_init(void)
{
        int i;

        hvsi_driver = alloc_tty_driver(hvsi_count);
        if (!hvsi_driver)
                return -ENOMEM;

        hvsi_driver->driver_name = "hvsi";
        hvsi_driver->name = "hvsi";
        hvsi_driver->major = HVSI_MAJOR;
        hvsi_driver->minor_start = HVSI_MINOR;
        hvsi_driver->type = TTY_DRIVER_TYPE_SYSTEM;
        hvsi_driver->init_termios = tty_std_termios;
        hvsi_driver->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL;
        hvsi_driver->init_termios.c_ispeed = 9600;
        hvsi_driver->init_termios.c_ospeed = 9600;
        hvsi_driver->flags = TTY_DRIVER_REAL_RAW;
        tty_set_operations(hvsi_driver, &hvsi_ops);

        for (i=0; i < hvsi_count; i++) {
                struct hvsi_struct *hp = &hvsi_ports[i];
                int ret = 1;

                tty_port_link_device(&hp->port, hvsi_driver, i);

                ret = request_irq(hp->virq, hvsi_interrupt, 0, "hvsi", hp);
                if (ret)
                        printk(KERN_ERR "HVSI: couldn't reserve irq 0x%x (error %i)\n",
                                hp->virq, ret);
        }
        hvsi_wait = wait_for_state; /* irqs active now */

        if (tty_register_driver(hvsi_driver))
                panic("Couldn't register hvsi console driver\n");

        printk(KERN_DEBUG "HVSI: registered %i devices\n", hvsi_count);

        return 0;
}
device_initcall(hvsi_init);

/***** console (not tty) code: *****/

static void hvsi_console_print(struct console *console, const char *buf,
                unsigned int count)
{
        struct hvsi_struct *hp = &hvsi_ports[console->index];
        char c[HVSI_MAX_OUTGOING_DATA] __ALIGNED__;
        unsigned int i = 0, n = 0;
        int ret, donecr = 0;

        mb();
        if (!is_open(hp))
                return;

        /*
         * ugh, we have to translate LF -> CRLF ourselves, in place.
         * copied from hvc_console.c:
         */
        while (count > 0 || i > 0) {
                if (count > 0 && i < sizeof(c)) {
                        if (buf[n] == '\n' && !donecr) {
                                c[i++] = '\r';
                                donecr = 1;
                        } else {
                                c[i++] = buf[n++];
                                donecr = 0;
                                --count;
                        }
                } else {
                        ret = hvsi_put_chars(hp, c, i);
                        if (ret < 0)
                                i = 0;
                        i -= ret;
                }
        }
}

static struct tty_driver *hvsi_console_device(struct console *console,
        int *index)
{
        *index = console->index;
        return hvsi_driver;
}

static int __init hvsi_console_setup(struct console *console, char *options)
{
        struct hvsi_struct *hp;
        int ret;

        if (console->index < 0 || console->index >= hvsi_count)
                return -1;
        hp = &hvsi_ports[console->index];

        /* give the FSP a chance to change the baud rate when we re-open */
        hvsi_close_protocol(hp);

        ret = hvsi_handshake(hp);
        if (ret < 0)
                return ret;

        ret = hvsi_get_mctrl(hp);
        if (ret < 0)
                return ret;

        ret = hvsi_set_mctrl(hp, hp->mctrl | TIOCM_DTR);
        if (ret < 0)
                return ret;

        hp->flags |= HVSI_CONSOLE;

        return 0;
}

static struct console hvsi_console = {
        .name           = "hvsi",
        .write          = hvsi_console_print,
        .device         = hvsi_console_device,
        .setup          = hvsi_console_setup,
        .flags          = CON_PRINTBUFFER,
        .index          = -1,
};

static int __init hvsi_console_init(void)
{
        struct device_node *vty;

        hvsi_wait = poll_for_state; /* no irqs yet; must poll */

        /* search device tree for vty nodes */
        for_each_compatible_node(vty, "serial", "hvterm-protocol") {
                struct hvsi_struct *hp;
                const __be32 *vtermno, *irq;

                vtermno = of_get_property(vty, "reg", NULL);
                irq = of_get_property(vty, "interrupts", NULL);
                if (!vtermno || !irq)
                        continue;

                if (hvsi_count >= MAX_NR_HVSI_CONSOLES) {
                        of_node_put(vty);
                        break;
                }

                hp = &hvsi_ports[hvsi_count];
                INIT_DELAYED_WORK(&hp->writer, hvsi_write_worker);
                INIT_WORK(&hp->handshaker, hvsi_handshaker);
                init_waitqueue_head(&hp->emptyq);
                init_waitqueue_head(&hp->stateq);
                spin_lock_init(&hp->lock);
                tty_port_init(&hp->port);
                hp->index = hvsi_count;
                hp->inbuf_end = hp->inbuf;
                hp->state = HVSI_CLOSED;
                hp->vtermno = be32_to_cpup(vtermno);
                hp->virq = irq_create_mapping(NULL, be32_to_cpup(irq));
                if (hp->virq == 0) {
                        printk(KERN_ERR "%s: couldn't create irq mapping for 0x%x\n",
                               __func__, be32_to_cpup(irq));
                        tty_port_destroy(&hp->port);
                        continue;
                }

                hvsi_count++;
        }

        if (hvsi_count)
                register_console(&hvsi_console);
        return 0;
}
console_initcall(hvsi_console_init);