virtio: console: comment cleanup

[linux-2.6-block.git] / drivers / char / virtio_console.c

/*
 * Copyright (C) 2006, 2007, 2009 Rusty Russell, IBM Corporation
 *
 * 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/err.h>
#include <linux/init.h>
#include <linux/virtio.h>
#include <linux/virtio_console.h>
#include "hvc_console.h"

static struct virtqueue *in_vq, *out_vq;
static struct virtio_device *vdev;

/* This is our input buffer, and how much data is left in it. */
static unsigned int in_len;
static char *in, *inbuf;

/* The operations for our console. */
static struct hv_ops virtio_cons;

/* The hvc device */
static struct hvc_struct *hvc;

/*
 * The put_chars() callback is pretty straightforward.
 *
 * We turn the characters into a scatter-gather list, add it to the
 * output queue and then kick the Host.  Then we sit here waiting for
 * it to finish: inefficient in theory, but in practice
 * implementations will do it immediately (lguest's Launcher does).
 */
static int put_chars(u32 vtermno, const char *buf, int count)
{
	struct scatterlist sg[1];
	unsigned int len;

	/* This is a convenient routine to initialize a single-elem sg list */
	sg_init_one(sg, buf, count);

	/*
	 * add_buf wants a token to identify this buffer: we hand it
	 * any non-NULL pointer, since there's only ever one buffer.
	 */
	if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) >= 0) {
		/* Tell Host to go! */
		out_vq->vq_ops->kick(out_vq);
		/* Chill out until it's done with the buffer. */
		while (!out_vq->vq_ops->get_buf(out_vq, &len))
			cpu_relax();
	}

	/* We're expected to return the amount of data we wrote: all of it. */
	return count;
}

/*
 * Create a scatter-gather list representing our input buffer and put
 * it in the queue.
 */
static void add_inbuf(void)
{
	struct scatterlist sg[1];
	sg_init_one(sg, inbuf, PAGE_SIZE);

	/* We should always be able to add one buffer to an empty queue. */
	if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) < 0)
		BUG();
	in_vq->vq_ops->kick(in_vq);
}

/*
 * get_chars() is the callback from the hvc_console infrastructure
 * when an interrupt is received.
 *
 * Most of the code deals with the fact that the hvc_console()
 * infrastructure only asks us for 16 bytes at a time.  We keep
 * in_offset and in_used fields for partially-filled buffers.
 */
static int get_chars(u32 vtermno, char *buf, int count)
{
	/* If we don't have an input queue yet, we can't get input. */
	BUG_ON(!in_vq);

	/* No buffer?  Try to get one. */
	if (!in_len) {
		in = in_vq->vq_ops->get_buf(in_vq, &in_len);
		if (!in)
			return 0;
	}

	/* You want more than we have to give?  Well, try wanting less! */
	if (in_len < count)
		count = in_len;

	/* Copy across to their buffer and increment offset. */
	memcpy(buf, in, count);
	in += count;
	in_len -= count;

	/* Finished?  Re-register buffer so Host will use it again. */
	if (in_len == 0)
		add_inbuf();

	return count;
}

/*
 * Console drivers are initialized very early so boot messages can go
 * out, so we do things slightly differently from the generic virtio
 * initialization of the net and block drivers.
 *
 * At this stage, the console is output-only.  It's too early to set
 * up a virtqueue, so we let the drivers do some boutique early-output
 * thing.
 */
int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int))
{
	virtio_cons.put_chars = put_chars;
	return hvc_instantiate(0, 0, &virtio_cons);
}

/*
 * virtio console configuration. This supports:
 * - console resize
 */
static void virtcons_apply_config(struct virtio_device *dev)
{
	struct winsize ws;

	if (virtio_has_feature(dev, VIRTIO_CONSOLE_F_SIZE)) {
		dev->config->get(dev,
				 offsetof(struct virtio_console_config, cols),
				 &ws.ws_col, sizeof(u16));
		dev->config->get(dev,
				 offsetof(struct virtio_console_config, rows),
				 &ws.ws_row, sizeof(u16));
		hvc_resize(hvc, ws);
	}
}

/*
 * we support only one console, the hvc struct is a global var We set
 * the configuration at this point, since we now have a tty
 */
static int notifier_add_vio(struct hvc_struct *hp, int data)
{
	hp->irq_requested = 1;
	virtcons_apply_config(vdev);

	return 0;
}

static void notifier_del_vio(struct hvc_struct *hp, int data)
{
	hp->irq_requested = 0;
}

static void hvc_handle_input(struct virtqueue *vq)
{
	if (hvc_poll(hvc))
		hvc_kick();
}

/*
 * Once we're further in boot, we get probed like any other virtio
 * device.  At this stage we set up the output virtqueue.
 *
 * To set up and manage our virtual console, we call hvc_alloc().
 * Since we never remove the console device we never need this pointer
 * again.
 *
 * Finally we put our input buffer in the input queue, ready to
 * receive.
 */
static int __devinit virtcons_probe(struct virtio_device *dev)
{
	vq_callback_t *callbacks[] = { hvc_handle_input, NULL};
	const char *names[] = { "input", "output" };
	struct virtqueue *vqs[2];
	int err;

	vdev = dev;

	/* This is the scratch page we use to receive console input */
	inbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!inbuf) {
		err = -ENOMEM;
		goto fail;
	}

	/* Find the queues. */
	err = vdev->config->find_vqs(vdev, 2, vqs, callbacks, names);
	if (err)
		goto free;

	in_vq = vqs[0];
	out_vq = vqs[1];

	/* Start using the new console output. */
	virtio_cons.get_chars = get_chars;
	virtio_cons.put_chars = put_chars;
	virtio_cons.notifier_add = notifier_add_vio;
	virtio_cons.notifier_del = notifier_del_vio;
	virtio_cons.notifier_hangup = notifier_del_vio;

	/*
	 * The first argument of hvc_alloc() is the virtual console
	 * number, so we use zero.  The second argument is the
	 * parameter for the notification mechanism (like irq
	 * number). We currently leave this as zero, virtqueues have
	 * implicit notifications.
	 *
	 * The third argument is a "struct hv_ops" containing the
	 * put_chars(), get_chars(), notifier_add() and notifier_del()
	 * pointers.  The final argument is the output buffer size: we
	 * can do any size, so we put PAGE_SIZE here.
	 */
	hvc = hvc_alloc(0, 0, &virtio_cons, PAGE_SIZE);
	if (IS_ERR(hvc)) {
		err = PTR_ERR(hvc);
		goto free_vqs;
	}

	/* Register the input buffer the first time. */
	add_inbuf();
	return 0;

free_vqs:
	vdev->config->del_vqs(vdev);
free:
	kfree(inbuf);
fail:
	return err;
}

static struct virtio_device_id id_table[] = {
	{ VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID },
	{ 0 },
};

static unsigned int features[] = {
	VIRTIO_CONSOLE_F_SIZE,
};

static struct virtio_driver virtio_console = {
	.feature_table = features,
	.feature_table_size = ARRAY_SIZE(features),
	.driver.name =	KBUILD_MODNAME,
	.driver.owner =	THIS_MODULE,
	.id_table =	id_table,
	.probe =	virtcons_probe,
	.config_changed = virtcons_apply_config,
};

static int __init init(void)
{
	return register_virtio_driver(&virtio_console);
}
module_init(init);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio console driver");
MODULE_LICENSE("GPL");