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hvsi.c

/*
 * Copyright (C) 2004 Hollis Blanchard <hollisb@us.ibm.com>, IBM
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 */

/* 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 <asm/uaccess.h>
#include <asm/vio.h>
#include <asm/param.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 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;
      struct tty_struct *tty;
      unsigned int count;
      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

#define VS_DATA_PACKET_HEADER           0xff
#define VS_CONTROL_PACKET_HEADER        0xfe
#define VS_QUERY_PACKET_HEADER          0xfd
#define VS_QUERY_RESPONSE_PACKET_HEADER 0xfc

/* control verbs */
#define VSV_SET_MODEM_CTL    1 /* to service processor only */
#define VSV_MODEM_CTL_UPDATE 2 /* from service processor only */
#define VSV_CLOSE_PROTOCOL   3

/* query verbs */
#define VSV_SEND_VERSION_NUMBER 1
#define VSV_SEND_MODEM_CTL_STATUS 2

/* yes, these masks are not consecutive. */
#define HVSI_TSDTR 0x01
#define HVSI_TSCD  0x20

struct hvsi_header {
      uint8_t  type;
      uint8_t  len;
      uint16_t seqno;
} __attribute__((packed));

struct hvsi_data {
      uint8_t  type;
      uint8_t  len;
      uint16_t seqno;
      uint8_t  data[HVSI_MAX_OUTGOING_DATA];
} __attribute__((packed));

struct hvsi_control {
      uint8_t  type;
      uint8_t  len;
      uint16_t seqno;
      uint16_t verb;
      /* optional depending on verb: */
      uint32_t word;
      uint32_t mask;
} __attribute__((packed));

struct hvsi_query {
      uint8_t  type;
      uint8_t  len;
      uint16_t seqno;
      uint16_t verb;
} __attribute__((packed));

struct hvsi_query_response {
      uint8_t  type;
      uint8_t  len;
      uint16_t seqno;
      uint16_t verb;
      uint16_t query_seqno;
      union {
            uint8_t  version;
            uint32_t mctrl_word;
      } u;
} __attribute__((packed));



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 = state_names[hp->state];

      if (hp->state > ARRAY_SIZE(state_names))
            name = "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", __FUNCTION__, 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 **to_hangup, struct hvsi_struct **to_handshake)
{
      struct hvsi_control *header = (struct hvsi_control *)packet;

      switch (header->verb) {
            case VSV_MODEM_CTL_UPDATE:
                  if ((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 userland hasn't done an open(2) yet, hp->tty is NULL. */
                        if (hp->tty && !(hp->tty->flags & CLOCAL))
                              *to_hangup = hp->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;

      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;
                  if (resp->u.mctrl_word & HVSI_TSDTR)
                        hp->mctrl |= TIOCM_DTR;
                  if (resp->u.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.type = VS_QUERY_RESPONSE_PACKET_HEADER;
      packet.len = sizeof(struct hvsi_query_response);
      packet.seqno = atomic_inc_return(&hp->seqno);
      packet.verb = VSV_SEND_VERSION_NUMBER;
      packet.u.version = HVSI_VERSION;
      packet.query_seqno = query_seqno+1;

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

      wrote = hvc_put_chars(hp->vtermno, (char *)&packet, packet.len);
      if (wrote != packet.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, query->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->tty);
                  hp->sysrq = 0;
                  continue;
            }
#endif /* CONFIG_MAGIC_SYSRQ */
            tty_insert_flip_char(hp->tty, 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 struct tty_struct *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 NULL;

      if (overflow > 0) {
            pr_debug("%s: got >TTY_THRESHOLD_THROTTLE bytes\n", __FUNCTION__);
            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", __FUNCTION__);
            memcpy(hp->throttle_buf, data + TTY_THRESHOLD_THROTTLE, overflow);
            hp->n_throttle = overflow;
      }

      return hp->tty;
}

/*
 * 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 **flip,
            struct tty_struct **hangup, struct hvsi_struct **handshake)
{
      uint8_t *packet = hp->inbuf;
      int chunklen;

      *flip = NULL;
      *hangup = NULL;
      *handshake = NULL;

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

      pr_debug("%s: got %i bytes\n", __FUNCTION__, 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", __FUNCTION__,
                        len_packet(packet));
            dbg_dump_packet(packet);

            switch (header->type) {
                  case VS_DATA_PACKET_HEADER:
                        if (!is_open(hp))
                              break;
                        if (hp->tty == NULL)
                              break; /* no tty buffer to put data in */
                        *flip = hvsi_recv_data(hp, packet);
                        break;
                  case VS_CONTROL_PACKET_HEADER:
                        hvsi_recv_control(hp, packet, hangup, 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 (*hangup || *handshake) {
                  pr_debug("%s: hangup or handshake\n", __FUNCTION__);
                  /*
                   * we need to send the hangup now before receiving any more data.
                   * If we get "data, hangup, data", we can't deliver the second
                   * data before the hangup.
                   */
                  break;
            }
      }

      compact_inbuf(hp, packet);

      return 1;
}

static void hvsi_send_overflow(struct hvsi_struct *hp)
{
      pr_debug("%s: delivering %i bytes overflow\n", __FUNCTION__,
                  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 tty_struct *flip;
      struct tty_struct *hangup;
      struct hvsi_struct *handshake;
      unsigned long flags;
      int again = 1;

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

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

            /*
             * we have to call tty_flip_buffer_push() and tty_hangup() outside our
             * spinlock. But we also have to keep going until we've read all the
             * available data.
             */

            if (flip) {
                  /* there was data put in the tty flip buffer */
                  tty_flip_buffer_push(flip);
                  flip = NULL;
            }

            if (hangup) {
                  tty_hangup(hangup);
            }

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

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

      if (flip) {
            tty_flip_buffer_push(flip);
      }

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

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

      wrote = hvc_put_chars(hp->vtermno, (char *)&packet, packet.len);
      if (wrote != packet.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", __FUNCTION__, 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.type = VS_CONTROL_PACKET_HEADER,
      packet.seqno = atomic_inc_return(&hp->seqno);
      packet.len = sizeof(struct hvsi_control);
      packet.verb = VSV_SET_MODEM_CTL;
      packet.mask = HVSI_TSDTR;

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

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

      wrote = hvc_put_chars(hp->vtermno, (char *)&packet, packet.len);
      if (wrote != packet.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.type = VS_DATA_PACKET_HEADER;
      packet.seqno = atomic_inc_return(&hp->seqno);
      packet.len = count + sizeof(struct hvsi_header);
      memcpy(&packet.data, buf, count);

      ret = hvc_put_chars(hp->vtermno, (char *)&packet, packet.len);
      if (ret == packet.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.type = VS_CONTROL_PACKET_HEADER;
      packet.seqno = atomic_inc_return(&hp->seqno);
      packet.len = 6;
      packet.verb = VSV_CLOSE_PROTOCOL;

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

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

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

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

      if (line < 0 || line >= hvsi_count)
            return -ENODEV;
      hp = &hvsi_ports[line];

      tty->driver_data = hp;
      tty->low_latency = 1; /* avoid throttle/tty_flip_buffer_push race */

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

      spin_lock_irqsave(&hp->lock, flags);
      hp->tty = tty;
      hp->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(&hp->writer);
      flush_scheduled_work();

      /*
       * 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", __FUNCTION__);

      if (tty_hung_up_p(filp))
            return;

      spin_lock_irqsave(&hp->lock, flags);

      if (--hp->count == 0) {
            hp->tty = 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->count < 0)
            printk(KERN_ERR "hvsi_close %lu: oops, count is %d\n",
                   hp - hvsi_ports, hp->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", __FUNCTION__);

      spin_lock_irqsave(&hp->lock, flags);

      hp->count = 0;
      hp->n_outbuf = 0;
      hp->tty = NULL;

      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", __FUNCTION__, 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", __FUNCTION__, 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", __FUNCTION__,
                        jiffies - start_j);
            start_j = 0;
#endif /* DEBUG */
            wake_up_all(&hp->emptyq);
            tty_wakeup(hp->tty);
      }

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

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

      return N_OUTBUF - hp->n_outbuf;
}

static int hvsi_chars_in_buffer(struct tty_struct *tty)
{
      struct hvsi_struct *hp = (struct hvsi_struct *)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", __FUNCTION__, 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", __FUNCTION__);
            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(hp->tty) > 0)) {
            int chunksize = min(count, hvsi_write_room(hp->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", __FUNCTION__, 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 = (struct hvsi_struct *)tty->driver_data;

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

      h_vio_signal(hp->vtermno, VIO_IRQ_DISABLE);
}

static void hvsi_unthrottle(struct tty_struct *tty)
{
      struct hvsi_struct *hp = (struct hvsi_struct *)tty->driver_data;
      unsigned long flags;
      int shouldflip = 0;

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

      spin_lock_irqsave(&hp->lock, flags);
      if (hp->n_throttle) {
            hvsi_send_overflow(hp);
            shouldflip = 1;
      }
      spin_unlock_irqrestore(&hp->lock, flags);

      if (shouldflip)
            tty_flip_buffer_push(hp->tty);

      h_vio_signal(hp->vtermno, VIO_IRQ_ENABLE);
}

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

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

static int hvsi_tiocmset(struct tty_struct *tty, struct file *file,
            unsigned int set, unsigned int clear)
{
      struct hvsi_struct *hp = (struct hvsi_struct *)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->owner = THIS_MODULE;
      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;

            ret = request_irq(hp->virq, hvsi_interrupt, IRQF_DISABLED, "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 = &hvsi_ports[console->index];
      int ret;

      if (console->index < 0 || console->index >= hvsi_count)
            return -1;

      /* 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_con_driver = {
      .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 (vty = of_find_compatible_node(NULL, "serial", "hvterm-protocol");
                  vty != NULL;
                  vty = of_find_compatible_node(vty, "serial", "hvterm-protocol")) {
            struct hvsi_struct *hp;
            const uint32_t *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);
            hp->index = hvsi_count;
            hp->inbuf_end = hp->inbuf;
            hp->state = HVSI_CLOSED;
            hp->vtermno = *vtermno;
            hp->virq = irq_create_mapping(NULL, irq[0]);
            if (hp->virq == NO_IRQ) {
                  printk(KERN_ERR "%s: couldn't create irq mapping for 0x%x\n",
                        __FUNCTION__, irq[0]);
                  continue;
            }

            hvsi_count++;
      }

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

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