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hvc_console.c

/*
 * Copyright (C) 2001 Anton Blanchard <anton@au.ibm.com>, IBM
 * Copyright (C) 2001 Paul Mackerras <paulus@au.ibm.com>, IBM
 * Copyright (C) 2004 Benjamin Herrenschmidt <benh@kernel.crashing.org>, IBM Corp.
 * Copyright (C) 2004 IBM Corporation
 *
 * Additional Author(s):
 *  Ryan S. Arnold <rsa@us.ibm.com>
 *
 * 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
 */

#include <linux/console.h>
#include <linux/cpumask.h>
#include <linux/init.h>
#include <linux/kbd_kern.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/major.h>
#include <linux/sysrq.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/delay.h>
#include <linux/freezer.h>

#include <asm/uaccess.h>

#include "hvc_console.h"

#define HVC_MAJOR 229
#define HVC_MINOR 0

/*
 * Wait this long per iteration while trying to push buffered data to the
 * hypervisor before allowing the tty to complete a close operation.
 */
#define HVC_CLOSE_WAIT (HZ/100) /* 1/10 of a second */

/*
 * These sizes are most efficient for vio, because they are the
 * native transfer size. We could make them selectable in the
 * future to better deal with backends that want other buffer sizes.
 */
#define N_OUTBUF  16
#define N_INBUF         16

#define __ALIGNED__ __attribute__((__aligned__(sizeof(long))))

static struct tty_driver *hvc_driver;
static struct task_struct *hvc_task;

/* Picks up late kicks after list walk but before schedule() */
static int hvc_kicked;

static int hvc_init(void);

#ifdef CONFIG_MAGIC_SYSRQ
static int sysrq_pressed;
#endif

struct hvc_struct {
      spinlock_t lock;
      int index;
      struct tty_struct *tty;
      unsigned int count;
      int do_wakeup;
      char *outbuf;
      int outbuf_size;
      int n_outbuf;
      uint32_t vtermno;
      struct hv_ops *ops;
      int irq_requested;
      int irq;
      struct list_head next;
      struct kobject kobj; /* ref count & hvc_struct lifetime */
};

/* dynamic list of hvc_struct instances */
static struct list_head hvc_structs = LIST_HEAD_INIT(hvc_structs);

/*
 * Protect the list of hvc_struct instances from inserts and removals during
 * list traversal.
 */
static DEFINE_SPINLOCK(hvc_structs_lock);

/*
 * This value is used to assign a tty->index value to a hvc_struct based
 * upon order of exposure via hvc_probe(), when we can not match it to
 * a console candidate registered with hvc_instantiate().
 */
static int last_hvc = -1;

/*
 * Do not call this function with either the hvc_structs_lock or the hvc_struct
 * lock held.  If successful, this function increments the kobject reference
 * count against the target hvc_struct so it should be released when finished.
 */
static struct hvc_struct *hvc_get_by_index(int index)
{
      struct hvc_struct *hp;
      unsigned long flags;

      spin_lock(&hvc_structs_lock);

      list_for_each_entry(hp, &hvc_structs, next) {
            spin_lock_irqsave(&hp->lock, flags);
            if (hp->index == index) {
                  kobject_get(&hp->kobj);
                  spin_unlock_irqrestore(&hp->lock, flags);
                  spin_unlock(&hvc_structs_lock);
                  return hp;
            }
            spin_unlock_irqrestore(&hp->lock, flags);
      }
      hp = NULL;

      spin_unlock(&hvc_structs_lock);
      return hp;
}


/*
 * Initial console vtermnos for console API usage prior to full console
 * initialization.  Any vty adapter outside this range will not have usable
 * console interfaces but can still be used as a tty device.  This has to be
 * static because kmalloc will not work during early console init.
 */
static struct hv_ops *cons_ops[MAX_NR_HVC_CONSOLES];
static uint32_t vtermnos[MAX_NR_HVC_CONSOLES] =
      {[0 ... MAX_NR_HVC_CONSOLES - 1] = -1};

/*
 * Console APIs, NOT TTY.  These APIs are available immediately when
 * hvc_console_setup() finds adapters.
 */

static void hvc_console_print(struct console *co, const char *b,
                        unsigned count)
{
      char c[N_OUTBUF] __ALIGNED__;
      unsigned i = 0, n = 0;
      int r, donecr = 0, index = co->index;

      /* Console access attempt outside of acceptable console range. */
      if (index >= MAX_NR_HVC_CONSOLES)
            return;

      /* This console adapter was removed so it is not usable. */
      if (vtermnos[index] < 0)
            return;

      while (count > 0 || i > 0) {
            if (count > 0 && i < sizeof(c)) {
                  if (b[n] == '\n' && !donecr) {
                        c[i++] = '\r';
                        donecr = 1;
                  } else {
                        c[i++] = b[n++];
                        donecr = 0;
                        --count;
                  }
            } else {
                  r = cons_ops[index]->put_chars(vtermnos[index], c, i);
                  if (r < 0) {
                        /* throw away chars on error */
                        i = 0;
                  } else if (r > 0) {
                        i -= r;
                        if (i > 0)
                              memmove(c, c+r, i);
                  }
            }
      }
}

static struct tty_driver *hvc_console_device(struct console *c, int *index)
{
      if (vtermnos[c->index] == -1)
            return NULL;

      *index = c->index;
      return hvc_driver;
}

static int __init hvc_console_setup(struct console *co, char *options)
{
      if (co->index < 0 || co->index >= MAX_NR_HVC_CONSOLES)
            return -ENODEV;

      if (vtermnos[co->index] == -1)
            return -ENODEV;

      return 0;
}

static struct console hvc_con_driver = {
      .name       = "hvc",
      .write            = hvc_console_print,
      .device           = hvc_console_device,
      .setup            = hvc_console_setup,
      .flags            = CON_PRINTBUFFER,
      .index            = -1,
};

/*
 * Early console initialization.  Precedes driver initialization.
 *
 * (1) we are first, and the user specified another driver
 * -- index will remain -1
 * (2) we are first and the user specified no driver
 * -- index will be set to 0, then we will fail setup.
 * (3)  we are first and the user specified our driver
 * -- index will be set to user specified driver, and we will fail
 * (4) we are after driver, and this initcall will register us
 * -- if the user didn't specify a driver then the console will match
 *
 * Note that for cases 2 and 3, we will match later when the io driver
 * calls hvc_instantiate() and call register again.
 */
static int __init hvc_console_init(void)
{
      register_console(&hvc_con_driver);
      return 0;
}
console_initcall(hvc_console_init);

/*
 * hvc_instantiate() is an early console discovery method which locates
 * consoles * prior to the vio subsystem discovering them.  Hotplugged
 * vty adapters do NOT get an hvc_instantiate() callback since they
 * appear after early console init.
 */
int hvc_instantiate(uint32_t vtermno, int index, struct hv_ops *ops)
{
      struct hvc_struct *hp;

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

      if (vtermnos[index] != -1)
            return -1;

      /* make sure no no tty has been registered in this index */
      hp = hvc_get_by_index(index);
      if (hp) {
            kobject_put(&hp->kobj);
            return -1;
      }

      vtermnos[index] = vtermno;
      cons_ops[index] = ops;

      /* reserve all indices up to and including this index */
      if (last_hvc < index)
            last_hvc = index;

      /* if this index is what the user requested, then register
       * now (setup won't fail at this point).  It's ok to just
       * call register again if previously .setup failed.
       */
      if (index == hvc_con_driver.index)
            register_console(&hvc_con_driver);

      return 0;
}

/* Wake the sleeping khvcd */
static void hvc_kick(void)
{
      hvc_kicked = 1;
      wake_up_process(hvc_task);
}

static int hvc_poll(struct hvc_struct *hp);

/*
 * NOTE: This API isn't used if the console adapter doesn't support interrupts.
 * In this case the console is poll driven.
 */
static irqreturn_t hvc_handle_interrupt(int irq, void *dev_instance)
{
      /* if hvc_poll request a repoll, then kick the hvcd thread */
      if (hvc_poll(dev_instance))
            hvc_kick();
      return IRQ_HANDLED;
}

static void hvc_unthrottle(struct tty_struct *tty)
{
      hvc_kick();
}

/*
 * The TTY interface won't be used until after the vio layer has exposed the vty
 * adapter to the kernel.
 */
static int hvc_open(struct tty_struct *tty, struct file * filp)
{
      struct hvc_struct *hp;
      unsigned long flags;
      int irq = 0;
      int rc = 0;
      struct kobject *kobjp;

      /* Auto increments kobject reference if found. */
      if (!(hp = hvc_get_by_index(tty->index)))
            return -ENODEV;

      spin_lock_irqsave(&hp->lock, flags);
      /* Check and then increment for fast path open. */
      if (hp->count++ > 0) {
            spin_unlock_irqrestore(&hp->lock, flags);
            hvc_kick();
            return 0;
      } /* else count == 0 */

      tty->driver_data = hp;
      tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */

      hp->tty = tty;
      /* Save for request_irq outside of spin_lock. */
      irq = hp->irq;
      if (irq)
            hp->irq_requested = 1;

      kobjp = &hp->kobj;

      spin_unlock_irqrestore(&hp->lock, flags);
      /* check error, fallback to non-irq */
      if (irq)
            rc = request_irq(irq, hvc_handle_interrupt, IRQF_DISABLED, "hvc_console", hp);

      /*
       * If the request_irq() fails and we return an error.  The tty layer
       * will call hvc_close() after a failed open but we don't want to clean
       * up there so we'll clean up here and clear out the previously set
       * tty fields and return the kobject reference.
       */
      if (rc) {
            spin_lock_irqsave(&hp->lock, flags);
            hp->tty = NULL;
            hp->irq_requested = 0;
            spin_unlock_irqrestore(&hp->lock, flags);
            tty->driver_data = NULL;
            kobject_put(kobjp);
            printk(KERN_ERR "hvc_open: request_irq failed with rc %d.\n", rc);
      }
      /* Force wakeup of the polling thread */
      hvc_kick();

      return rc;
}

static void hvc_close(struct tty_struct *tty, struct file * filp)
{
      struct hvc_struct *hp;
      struct kobject *kobjp;
      int irq = 0;
      unsigned long flags;

      if (tty_hung_up_p(filp))
            return;

      /*
       * No driver_data means that this close was issued after a failed
       * hvc_open by the tty layer's release_dev() function and we can just
       * exit cleanly because the kobject reference wasn't made.
       */
      if (!tty->driver_data)
            return;

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

      kobjp = &hp->kobj;
      if (--hp->count == 0) {
            if (hp->irq_requested)
                  irq = hp->irq;
            hp->irq_requested = 0;

            /* We are done with the tty pointer now. */
            hp->tty = NULL;
            spin_unlock_irqrestore(&hp->lock, flags);

            /*
             * Chain calls chars_in_buffer() and returns immediately if
             * there is no buffered data otherwise sleeps on a wait queue
             * waking periodically to check chars_in_buffer().
             */
            tty_wait_until_sent(tty, HVC_CLOSE_WAIT);

            if (irq)
                  free_irq(irq, hp);

      } else {
            if (hp->count < 0)
                  printk(KERN_ERR "hvc_close %X: oops, count is %d\n",
                        hp->vtermno, hp->count);
            spin_unlock_irqrestore(&hp->lock, flags);
      }

      kobject_put(kobjp);
}

static void hvc_hangup(struct tty_struct *tty)
{
      struct hvc_struct *hp = tty->driver_data;
      unsigned long flags;
      int irq = 0;
      int temp_open_count;
      struct kobject *kobjp;

      if (!hp)
            return;

      spin_lock_irqsave(&hp->lock, flags);

      /*
       * The N_TTY line discipline has problems such that in a close vs
       * open->hangup case this can be called after the final close so prevent
       * that from happening for now.
       */
      if (hp->count <= 0) {
            spin_unlock_irqrestore(&hp->lock, flags);
            return;
      }

      kobjp = &hp->kobj;
      temp_open_count = hp->count;
      hp->count = 0;
      hp->n_outbuf = 0;
      hp->tty = NULL;
      if (hp->irq_requested)
            /* Saved for use outside of spin_lock. */
            irq = hp->irq;
      hp->irq_requested = 0;
      spin_unlock_irqrestore(&hp->lock, flags);
      if (irq)
            free_irq(irq, hp);
      while(temp_open_count) {
            --temp_open_count;
            kobject_put(kobjp);
      }
}

/*
 * Push buffered characters whether they were just recently buffered or waiting
 * on a blocked hypervisor.  Call this function with hp->lock held.
 */
static void hvc_push(struct hvc_struct *hp)
{
      int n;

      n = hp->ops->put_chars(hp->vtermno, hp->outbuf, hp->n_outbuf);
      if (n <= 0) {
            if (n == 0) {
                  hp->do_wakeup = 1;
                  return;
            }
            /* throw away output on error; this happens when
               there is no session connected to the vterm. */
            hp->n_outbuf = 0;
      } else
            hp->n_outbuf -= n;
      if (hp->n_outbuf > 0)
            memmove(hp->outbuf, hp->outbuf + n, hp->n_outbuf);
      else
            hp->do_wakeup = 1;
}

static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count)
{
      struct hvc_struct *hp = tty->driver_data;
      unsigned long flags;
      int rsize, written = 0;

      /* This write was probably executed during a tty close. */
      if (!hp)
            return -EPIPE;

      if (hp->count <= 0)
            return -EIO;

      spin_lock_irqsave(&hp->lock, flags);

      /* Push pending writes */
      if (hp->n_outbuf > 0)
            hvc_push(hp);

      while (count > 0 && (rsize = hp->outbuf_size - hp->n_outbuf) > 0) {
            if (rsize > count)
                  rsize = count;
            memcpy(hp->outbuf + hp->n_outbuf, buf, rsize);
            count -= rsize;
            buf += rsize;
            hp->n_outbuf += rsize;
            written += rsize;
            hvc_push(hp);
      }
      spin_unlock_irqrestore(&hp->lock, flags);

      /*
       * Racy, but harmless, kick thread if there is still pending data.
       */
      if (hp->n_outbuf)
            hvc_kick();

      return written;
}

/*
 * This is actually a contract between the driver and the tty layer outlining
 * how much write room the driver can guarantee will be sent OR BUFFERED.  This
 * driver MUST honor the return value.
 */
static int hvc_write_room(struct tty_struct *tty)
{
      struct hvc_struct *hp = tty->driver_data;

      if (!hp)
            return -1;

      return hp->outbuf_size - hp->n_outbuf;
}

static int hvc_chars_in_buffer(struct tty_struct *tty)
{
      struct hvc_struct *hp = tty->driver_data;

      if (!hp)
            return -1;
      return hp->n_outbuf;
}

/*
 * timeout will vary between the MIN and MAX values defined here.  By default
 * and during console activity we will use a default MIN_TIMEOUT of 10.  When
 * the console is idle, we increase the timeout value on each pass through
 * msleep until we reach the max.  This may be noticeable as a brief (average
 * one second) delay on the console before the console responds to input when
 * there has been no input for some time.
 */
#define MIN_TIMEOUT           (10)
#define MAX_TIMEOUT           (2000)
static u32 timeout = MIN_TIMEOUT;

#define HVC_POLL_READ   0x00000001
#define HVC_POLL_WRITE  0x00000002

static int hvc_poll(struct hvc_struct *hp)
{
      struct tty_struct *tty;
      int i, n, poll_mask = 0;
      char buf[N_INBUF] __ALIGNED__;
      unsigned long flags;
      int read_total = 0;

      spin_lock_irqsave(&hp->lock, flags);

      /* Push pending writes */
      if (hp->n_outbuf > 0)
            hvc_push(hp);

      /* Reschedule us if still some write pending */
      if (hp->n_outbuf > 0)
            poll_mask |= HVC_POLL_WRITE;

      /* No tty attached, just skip */
      tty = hp->tty;
      if (tty == NULL)
            goto bail;

      /* Now check if we can get data (are we throttled ?) */
      if (test_bit(TTY_THROTTLED, &tty->flags))
            goto throttled;

      /* If we aren't interrupt driven and aren't throttled, we always
       * request a reschedule
       */
      if (hp->irq == 0)
            poll_mask |= HVC_POLL_READ;

      /* Read data if any */
      for (;;) {
            int count = tty_buffer_request_room(tty, N_INBUF);

            /* If flip is full, just reschedule a later read */
            if (count == 0) {
                  poll_mask |= HVC_POLL_READ;
                  break;
            }

            n = hp->ops->get_chars(hp->vtermno, buf, count);
            if (n <= 0) {
                  /* Hangup the tty when disconnected from host */
                  if (n == -EPIPE) {
                        spin_unlock_irqrestore(&hp->lock, flags);
                        tty_hangup(tty);
                        spin_lock_irqsave(&hp->lock, flags);
                  } else if ( n == -EAGAIN ) {
                        /*
                         * Some back-ends can only ensure a certain min
                         * num of bytes read, which may be > 'count'.
                         * Let the tty clear the flip buff to make room.
                         */
                        poll_mask |= HVC_POLL_READ;
                  }
                  break;
            }
            for (i = 0; i < n; ++i) {
#ifdef CONFIG_MAGIC_SYSRQ
                  if (hp->index == hvc_con_driver.index) {
                        /* Handle the SysRq Hack */
                        /* XXX should support a sequence */
                        if (buf[i] == '\x0f') { /* ^O */
                              sysrq_pressed = 1;
                              continue;
                        } else if (sysrq_pressed) {
                              handle_sysrq(buf[i], tty);
                              sysrq_pressed = 0;
                              continue;
                        }
                  }
#endif /* CONFIG_MAGIC_SYSRQ */
                  tty_insert_flip_char(tty, buf[i], 0);
            }

            read_total += n;
      }
 throttled:
      /* Wakeup write queue if necessary */
      if (hp->do_wakeup) {
            hp->do_wakeup = 0;
            tty_wakeup(tty);
      }
 bail:
      spin_unlock_irqrestore(&hp->lock, flags);

      if (read_total) {
            /* Activity is occurring, so reset the polling backoff value to
               a minimum for performance. */
            timeout = MIN_TIMEOUT;

            tty_flip_buffer_push(tty);
      }

      return poll_mask;
}

#if defined(CONFIG_XMON) && defined(CONFIG_SMP)
extern cpumask_t cpus_in_xmon;
#else
static const cpumask_t cpus_in_xmon = CPU_MASK_NONE;
#endif

/*
 * This kthread is either polling or interrupt driven.  This is determined by
 * calling hvc_poll() who determines whether a console adapter support
 * interrupts.
 */
static int khvcd(void *unused)
{
      int poll_mask;
      struct hvc_struct *hp;

      set_freezable();
      __set_current_state(TASK_RUNNING);
      do {
            poll_mask = 0;
            hvc_kicked = 0;
            try_to_freeze();
            wmb();
            if (cpus_empty(cpus_in_xmon)) {
                  spin_lock(&hvc_structs_lock);
                  list_for_each_entry(hp, &hvc_structs, next) {
                        poll_mask |= hvc_poll(hp);
                  }
                  spin_unlock(&hvc_structs_lock);
            } else
                  poll_mask |= HVC_POLL_READ;
            if (hvc_kicked)
                  continue;
            if (poll_mask & HVC_POLL_WRITE) {
                  yield();
                  continue;
            }
            set_current_state(TASK_INTERRUPTIBLE);
            if (!hvc_kicked) {
                  if (poll_mask == 0)
                        schedule();
                  else {
                        if (timeout < MAX_TIMEOUT)
                              timeout += (timeout >> 6) + 1;

                        msleep_interruptible(timeout);
                  }
            }
            __set_current_state(TASK_RUNNING);
      } while (!kthread_should_stop());

      return 0;
}

static const struct tty_operations hvc_ops = {
      .open = hvc_open,
      .close = hvc_close,
      .write = hvc_write,
      .hangup = hvc_hangup,
      .unthrottle = hvc_unthrottle,
      .write_room = hvc_write_room,
      .chars_in_buffer = hvc_chars_in_buffer,
};

/* callback when the kboject ref count reaches zero. */
static void destroy_hvc_struct(struct kobject *kobj)
{
      struct hvc_struct *hp = container_of(kobj, struct hvc_struct, kobj);
      unsigned long flags;

      spin_lock(&hvc_structs_lock);

      spin_lock_irqsave(&hp->lock, flags);
      list_del(&(hp->next));
      spin_unlock_irqrestore(&hp->lock, flags);

      spin_unlock(&hvc_structs_lock);

      kfree(hp);
}

static struct kobj_type hvc_kobj_type = {
      .release = destroy_hvc_struct,
};

struct hvc_struct __devinit *hvc_alloc(uint32_t vtermno, int irq,
                              struct hv_ops *ops, int outbuf_size)
{
      struct hvc_struct *hp;
      int i;

      /* We wait until a driver actually comes along */
      if (!hvc_driver) {
            int err = hvc_init();
            if (err)
                  return ERR_PTR(err);
      }

      hp = kmalloc(ALIGN(sizeof(*hp), sizeof(long)) + outbuf_size,
                  GFP_KERNEL);
      if (!hp)
            return ERR_PTR(-ENOMEM);

      memset(hp, 0x00, sizeof(*hp));

      hp->vtermno = vtermno;
      hp->irq = irq;
      hp->ops = ops;
      hp->outbuf_size = outbuf_size;
      hp->outbuf = &((char *)hp)[ALIGN(sizeof(*hp), sizeof(long))];

      kobject_init(&hp->kobj);
      hp->kobj.ktype = &hvc_kobj_type;

      spin_lock_init(&hp->lock);
      spin_lock(&hvc_structs_lock);

      /*
       * find index to use:
       * see if this vterm id matches one registered for console.
       */
      for (i=0; i < MAX_NR_HVC_CONSOLES; i++)
            if (vtermnos[i] == hp->vtermno &&
                cons_ops[i] == hp->ops)
                  break;

      /* no matching slot, just use a counter */
      if (i >= MAX_NR_HVC_CONSOLES)
            i = ++last_hvc;

      hp->index = i;

      list_add_tail(&(hp->next), &hvc_structs);
      spin_unlock(&hvc_structs_lock);

      return hp;
}

int __devexit hvc_remove(struct hvc_struct *hp)
{
      unsigned long flags;
      struct kobject *kobjp;
      struct tty_struct *tty;

      spin_lock_irqsave(&hp->lock, flags);
      tty = hp->tty;
      kobjp = &hp->kobj;

      if (hp->index < MAX_NR_HVC_CONSOLES)
            vtermnos[hp->index] = -1;

      /* Don't whack hp->irq because tty_hangup() will need to free the irq. */

      spin_unlock_irqrestore(&hp->lock, flags);

      /*
       * We 'put' the instance that was grabbed when the kobject instance
       * was initialized using kobject_init().  Let the last holder of this
       * kobject cause it to be removed, which will probably be the tty_hangup
       * below.
       */
      kobject_put(kobjp);

      /*
       * This function call will auto chain call hvc_hangup.  The tty should
       * always be valid at this time unless a simultaneous tty close already
       * cleaned up the hvc_struct.
       */
      if (tty)
            tty_hangup(tty);
      return 0;
}

/* Driver initialization: called as soon as someone uses hvc_alloc(). */
static int hvc_init(void)
{
      struct tty_driver *drv;
      int err;

      /* We need more than hvc_count adapters due to hotplug additions. */
      drv = alloc_tty_driver(HVC_ALLOC_TTY_ADAPTERS);
      if (!drv) {
            err = -ENOMEM;
            goto out;
      }

      drv->owner = THIS_MODULE;
      drv->driver_name = "hvc";
      drv->name = "hvc";
      drv->major = HVC_MAJOR;
      drv->minor_start = HVC_MINOR;
      drv->type = TTY_DRIVER_TYPE_SYSTEM;
      drv->init_termios = tty_std_termios;
      drv->flags = TTY_DRIVER_REAL_RAW;
      tty_set_operations(drv, &hvc_ops);

      /* Always start the kthread because there can be hotplug vty adapters
       * added later. */
      hvc_task = kthread_run(khvcd, NULL, "khvcd");
      if (IS_ERR(hvc_task)) {
            printk(KERN_ERR "Couldn't create kthread for console.\n");
            err = PTR_ERR(hvc_task);
            goto put_tty;
      }

      err = tty_register_driver(drv);
      if (err) {
            printk(KERN_ERR "Couldn't register hvc console driver\n");
            goto stop_thread;
      }

      /* FIXME: This mb() seems completely random.  Remove it. */
      mb();
      hvc_driver = drv;
      return 0;

put_tty:
      put_tty_driver(hvc_driver);
stop_thread:
      kthread_stop(hvc_task);
      hvc_task = NULL;
out:
      return err;
}

/* This isn't particularly necessary due to this being a console driver
 * but it is nice to be thorough.
 */
static void __exit hvc_exit(void)
{
      if (hvc_driver) {
            kthread_stop(hvc_task);

            tty_unregister_driver(hvc_driver);
            /* return tty_struct instances allocated in hvc_init(). */
            put_tty_driver(hvc_driver);
            unregister_console(&hvc_con_driver);
      }
}
module_exit(hvc_exit);

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