drivers/char/hvc_console.c - kernel/msm-4.9 - Gitiles

 /*
  * 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/config.h>
 #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 <asm/uaccess.h>

 #include "hvc_console.h"

 #define HVC_MAJOR	229
 #define HVC_MINOR	0

 #define TIMEOUT		(10)

 /*
  * 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;

 #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[N_OUTBUF] __ALIGNED__;
 	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 canidate registered with hvc_instantiate().
  */
 static int last_hvc = -1;

 /*
  * Do not call this function with either the hvc_strucst_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.
  */
 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.
  */

 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 useable. */
 	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;
 }

 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.  Preceeds 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 registerd 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 upto 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;
 }
 EXPORT_SYMBOL(hvc_instantiate);

 /* 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, struct pt_regs *regs)
 {
 	/* 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 = NO_IRQ;
 	int rc = 0;
 	struct kobject *kobjp;

 	/* Auto increments kobject reference if found. */
 	if (!(hp = hvc_get_by_index(tty->index))) {
 		printk(KERN_WARNING "hvc_console: tty open failed, no vty associated with tty.\n");
 		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 != NO_IRQ)
 		hp->irq_requested = 1;

 	kobjp = &hp->kobj;

 	spin_unlock_irqrestore(&hp->lock, flags);
 	/* check error, fallback to non-irq */
 	if (irq != NO_IRQ)
 		rc = request_irq(irq, hvc_handle_interrupt, SA_INTERRUPT, "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 = NO_IRQ;
 	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 != NO_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 = NO_IRQ;
 	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 != NO_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 = N_OUTBUF - 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 guarentee 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 N_OUTBUF - 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;
 }

 #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 == NO_IRQ)
 		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], NULL, 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)
 		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.
  */
 int khvcd(void *unused)
 {
 	int poll_mask;
 	struct hvc_struct *hp;

 	__set_current_state(TASK_RUNNING);
 	do {
 		poll_mask = 0;
 		hvc_kicked = 0;
 		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
 				msleep_interruptible(TIMEOUT);
 		}
 		__set_current_state(TASK_RUNNING);
 	} while (!kthread_should_stop());

 	return 0;
 }

 static 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)
 {
 	struct hvc_struct *hp;
 	int i;

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

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

 	hp->vtermno = vtermno;
 	hp->irq = irq;
 	hp->ops = ops;

 	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;
 }
 EXPORT_SYMBOL(hvc_alloc);

 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 intialized 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;
 }
 EXPORT_SYMBOL(hvc_remove);

 /* Driver initialization.  Follow console initialization.  This is where the TTY
  * interfaces start to become available. */
 int __init hvc_init(void)
 {
 	struct tty_driver *drv;

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

 	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)) {
 		panic("Couldn't create kthread for console.\n");
 		put_tty_driver(drv);
 		return -EIO;
 	}

 	if (tty_register_driver(drv))
 		panic("Couldn't register hvc console driver\n");

 	mb();
 	hvc_driver = drv;
 	return 0;
 }
 module_init(hvc_init);

 /* This isn't particularily necessary due to this being a console driver
  * but it is nice to be thorough.
  */
 static void __exit hvc_exit(void)
 {
 	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);
	/*
	* 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/config.h>
	#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 <asm/uaccess.h>

	#include "hvc_console.h"

	#define HVC_MAJOR 229
	#define HVC_MINOR 0

	#define TIMEOUT (10)

	/*
	* 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;

	#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[N_OUTBUF] __ALIGNED__;
	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 canidate registered with hvc_instantiate().
	*/
	static int last_hvc = -1;

	/*
	* Do not call this function with either the hvc_strucst_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.
	*/
	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.
	*/

	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 useable. */
	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;
	}

	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. Preceeds 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 registerd 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 upto 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;
	}
	EXPORT_SYMBOL(hvc_instantiate);

	/* 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, struct pt_regs regs)
	{
	/* 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 = NO_IRQ;
	int rc = 0;
	struct kobject *kobjp;

	/* Auto increments kobject reference if found. */
	if (!(hp = hvc_get_by_index(tty->index))) {
	printk(KERN_WARNING "hvc_console: tty open failed, no vty associated with tty.\n");
	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 != NO_IRQ)
	hp->irq_requested = 1;

	kobjp = &hp->kobj;

	spin_unlock_irqrestore(&hp->lock, flags);
	/* check error, fallback to non-irq */
	if (irq != NO_IRQ)
	rc = request_irq(irq, hvc_handle_interrupt, SA_INTERRUPT, "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 = NO_IRQ;
	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 != NO_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 = NO_IRQ;
	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 != NO_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 = N_OUTBUF - 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 guarentee 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 N_OUTBUF - 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;
	}

	#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 == NO_IRQ)
	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], NULL, 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)
	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.
	*/
	int khvcd(void *unused)
	{
	int poll_mask;
	struct hvc_struct *hp;

	__set_current_state(TASK_RUNNING);
	do {
	poll_mask = 0;
	hvc_kicked = 0;
	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
	msleep_interruptible(TIMEOUT);
	}
	__set_current_state(TASK_RUNNING);
	} while (!kthread_should_stop());

	return 0;
	}

	static 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)
	{
	struct hvc_struct *hp;
	int i;

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

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

	hp->vtermno = vtermno;
	hp->irq = irq;
	hp->ops = ops;

	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;
	}
	EXPORT_SYMBOL(hvc_alloc);

	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 intialized 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;
	}
	EXPORT_SYMBOL(hvc_remove);

	/* Driver initialization. Follow console initialization. This is where the TTY
	* interfaces start to become available. */
	int __init hvc_init(void)
	{
	struct tty_driver *drv;

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

	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)) {
	panic("Couldn't create kthread for console.\n");
	put_tty_driver(drv);
	return -EIO;
	}

	if (tty_register_driver(drv))
	panic("Couldn't register hvc console driver\n");

	mb();
	hvc_driver = drv;
	return 0;
	}
	module_init(hvc_init);

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