Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 831 insertions, 0 deletions

diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
new file mode 100644
index 00000000000..88cd858f74d
--- /dev/null
+++ b/drivers/char/hvc_console.c
@@ -0,0 +1,831 @@
+/*
+ * 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 <asm/uaccess.h>
+#include <asm/hvconsole.h>
+#include <asm/vio.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 */
+
+/*
+ * The Linux TTY code does not support dynamic addition of tty derived devices
+ * so we need to know how many tty devices we might need when space is allocated
+ * for the tty device.  Since this driver supports hotplug of vty adapters we
+ * need to make sure we have enough allocated.
+ */
+#define HVC_ALLOC_TTY_ADAPTERS	8
+
+static struct tty_driver *hvc_driver;
+#ifdef CONFIG_MAGIC_SYSRQ
+static int sysrq_pressed;
+#endif
+
+#define N_OUTBUF	16
+#define N_INBUF		16
+
+#define __ALIGNED__	__attribute__((__aligned__(8)))
+
+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;
+	int irq_requested;
+	int irq;
+	struct list_head next;
+	struct kobject kobj; /* ref count & hvc_struct lifetime */
+	struct vio_dev *vdev;
+};
+
+/* 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);
+
+/*
+ * 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 uint32_t vtermnos[MAX_NR_HVC_CONSOLES];
+
+/* Used for accounting purposes */
+static int num_vterms = 0;
+
+static struct task_struct *hvc_task;
+
+/*
+ * This value is used to associate a tty->index value to a hvc_struct based
+ * upon order of exposure via hvc_probe().
+ */
+static int hvc_count = -1;
+
+/* Picks up late kicks after list walk but before schedule() */
+static int hvc_kicked;
+
+/* Wake the sleeping khvcd */
+static void hvc_kick(void)
+{
+	hvc_kicked = 1;
+	wake_up_process(hvc_task);
+}
+
+/*
+ * 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)
+{
+	hvc_kick();
+	return IRQ_HANDLED;
+}
+
+static void hvc_unthrottle(struct tty_struct *tty)
+{
+	hvc_kick();
+}
+
+/*
+ * 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;
+}
+
+/*
+ * 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;
+	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 = hvc_put_chars(hp->vtermno, hp->outbuf, hp->n_outbuf);
+	if (n <= 0) {
+		if (n == 0)
+			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 inline int __hvc_write_kernel(struct hvc_struct *hp,
+				   const unsigned char *buf, int count)
+{
+	unsigned long flags;
+	int rsize, written = 0;
+
+	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);
+
+	return written;
+}
+static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count)
+{
+	struct hvc_struct *hp = tty->driver_data;
+	int written;
+
+	/* This write was probably executed during a tty close. */
+	if (!hp)
+		return -EPIPE;
+
+	if (hp->count <= 0)
+		return -EIO;
+
+	written = __hvc_write_kernel(hp, buf, count);
+
+	/*
+	 * Racy, but harmless, kick thread if there is still pending data.
+	 * There really is nothing wrong with kicking the thread, even if there
+	 * is no buffered 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
+#define HVC_POLL_QUICK	0x00000004
+
+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 = N_INBUF;
+		if (count > (TTY_FLIPBUF_SIZE - tty->flip.count))
+			count = TTY_FLIPBUF_SIZE - tty->flip.count;
+
+		/* If flip is full, just reschedule a later read */
+		if (count == 0) {
+			poll_mask |= HVC_POLL_READ;
+			break;
+		}
+
+		n = hvc_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);
+			}
+			break;
+		}
+		for (i = 0; i < n; ++i) {
+#ifdef CONFIG_MAGIC_SYSRQ
+			/* Handle the SysRq Hack */
+			if (buf[i] == '\x0f') {	/* ^O -- should support a sequence */
+				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);
+		}
+
+		if (tty->flip.count)
+			tty_schedule_flip(tty);
+
+		/*
+		 * Account for the total amount read in one loop, and if above
+		 * 64 bytes, we do a quick schedule loop to let the tty grok the
+		 * data and eventually throttle us.
+		 */
+		read_total += n;
+		if (read_total >= 64) {
+			poll_mask |= HVC_POLL_QUICK;
+			break;
+		}
+	}
+ throttled:
+	/* Wakeup write queue if necessary */
+	if (hp->do_wakeup) {
+		hp->do_wakeup = 0;
+		tty_wakeup(tty);
+	}
+ bail:
+	spin_unlock_irqrestore(&hp->lock, flags);
+
+	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) {
+				/*hp = list_entry(node, struct hvc_struct, * 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_QUICK) {
+			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,
+};
+
+char hvc_driver_name[] = "hvc_console";
+
+static struct vio_device_id hvc_driver_table[] __devinitdata= {
+	{"serial", "hvterm1"},
+	{ NULL, }
+};
+MODULE_DEVICE_TABLE(vio, hvc_driver_table);
+
+/* 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,
+};
+
+static int __devinit hvc_probe(
+		struct vio_dev *dev,
+		const struct vio_device_id *id)
+{
+	struct hvc_struct *hp;
+
+	/* probed with invalid parameters. */
+	if (!dev || !id)
+		return -EPERM;
+
+	hp = kmalloc(sizeof(*hp), GFP_KERNEL);
+	if (!hp)
+		return -ENOMEM;
+
+	memset(hp, 0x00, sizeof(*hp));
+	hp->vtermno = dev->unit_address;
+	hp->vdev = dev;
+	hp->vdev->dev.driver_data = hp;
+	hp->irq = dev->irq;
+
+	kobject_init(&hp->kobj);
+	hp->kobj.ktype = &hvc_kobj_type;
+
+	spin_lock_init(&hp->lock);
+	spin_lock(&hvc_structs_lock);
+	hp->index = ++hvc_count;
+	list_add_tail(&(hp->next), &hvc_structs);
+	spin_unlock(&hvc_structs_lock);
+
+	return 0;
+}
+
+static int __devexit hvc_remove(struct vio_dev *dev)
+{
+	struct hvc_struct *hp = dev->dev.driver_data;
+	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;
+}
+
+static struct vio_driver hvc_vio_driver = {
+	.name		= hvc_driver_name,
+	.id_table	= hvc_driver_table,
+	.probe		= hvc_probe,
+	.remove		= hvc_remove,
+};
+
+/* Driver initialization.  Follow console initialization.  This is where the TTY
+ * interfaces start to become available. */
+int __init hvc_init(void)
+{
+	int rc;
+
+	/* We need more than num_vterms adapters due to hotplug additions. */
+	hvc_driver = alloc_tty_driver(HVC_ALLOC_TTY_ADAPTERS);
+	/* hvc_driver = alloc_tty_driver(num_vterms); */
+	if (!hvc_driver)
+		return -ENOMEM;
+
+	hvc_driver->owner = THIS_MODULE;
+	hvc_driver->devfs_name = "hvc/";
+	hvc_driver->driver_name = "hvc";
+	hvc_driver->name = "hvc";
+	hvc_driver->major = HVC_MAJOR;
+	hvc_driver->minor_start = HVC_MINOR;
+	hvc_driver->type = TTY_DRIVER_TYPE_SYSTEM;
+	hvc_driver->init_termios = tty_std_termios;
+	hvc_driver->flags = TTY_DRIVER_REAL_RAW;
+	tty_set_operations(hvc_driver, &hvc_ops);
+
+	if (tty_register_driver(hvc_driver))
+		panic("Couldn't register hvc console driver\n");
+
+	/* 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(hvc_driver);
+		return -EIO;
+	}
+
+	/* Register as a vio device to receive callbacks */
+	rc = vio_register_driver(&hvc_vio_driver);
+
+	return rc;
+}
+
+/* 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);
+
+	vio_unregister_driver(&hvc_vio_driver);
+	tty_unregister_driver(hvc_driver);
+	/* return tty_struct instances allocated in hvc_init(). */
+	put_tty_driver(hvc_driver);
+}
+
+/*
+ * Console APIs, NOT TTY.  These APIs are available immediately when
+ * hvc_console_setup() finds adapters.
+ */
+
+/*
+ * 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 the appear after early console init.
+ */
+int hvc_instantiate(uint32_t vtermno, int index)
+{
+	if (index < 0 || index >= MAX_NR_HVC_CONSOLES)
+		return -1;
+
+	if (vtermnos[index] != -1)
+		return -1;
+
+	vtermnos[index] = vtermno;
+	return 0;
+}
+
+void hvc_console_print(struct console *co, const char *b, unsigned count)
+{
+	char c[16] __ALIGNED__;
+	unsigned i = 0, n = 0;
+	int r, donecr = 0;
+
+	/* Console access attempt outside of acceptable console range. */
+	if (co->index >= MAX_NR_HVC_CONSOLES)
+		return;
+
+	/* This console adapter was removed so it is not useable. */
+	if (vtermnos[co->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 = hvc_put_chars(vtermnos[co->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)
+{
+	*index = c->index;
+	return hvc_driver;
+}
+
+static int __init hvc_console_setup(struct console *co, char *options)
+{
+	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. */
+static int __init hvc_console_init(void)
+{
+	int i;
+
+	for (i=0; i<MAX_NR_HVC_CONSOLES; i++)
+		vtermnos[i] = -1;
+	num_vterms = hvc_find_vtys();
+	register_console(&hvc_con_driver);
+	return 0;
+}
+console_initcall(hvc_console_init);
+
+module_init(hvc_init);
+module_exit(hvc_exit);