1/*
2 * Randomness driver for virtio
3 *  Copyright (C) 2007, 2008 Rusty Russell IBM Corporation
4 *
5 *  This program is free software; you can redistribute it and/or modify
6 *  it under the terms of the GNU General Public License as published by
7 *  the Free Software Foundation; either version 2 of the License, or
8 *  (at your option) any later version.
9 *
10 *  This program is distributed in the hope that it will be useful,
11 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
12 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13 *  GNU General Public License for more details.
14 *
15 *  You should have received a copy of the GNU General Public License
16 *  along with this program; if not, write to the Free Software
17 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
18 */
19
20#include <linux/err.h>
21#include <linux/hw_random.h>
22#include <linux/scatterlist.h>
23#include <linux/spinlock.h>
24#include <linux/virtio.h>
25#include <linux/virtio_rng.h>
26#include <linux/module.h>
27
28static struct virtqueue *vq;
29static unsigned int data_avail;
30static DECLARE_COMPLETION(have_data);
31static bool busy;
32
33static void random_recv_done(struct virtqueue *vq)
34{
35	/* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
36	if (!virtqueue_get_buf(vq, &data_avail))
37		return;
38
39	complete(&have_data);
40}
41
42/* The host will fill any buffer we give it with sweet, sweet randomness. */
43static void register_buffer(u8 *buf, size_t size)
44{
45	struct scatterlist sg;
46
47	sg_init_one(&sg, buf, size);
48
49	/* There should always be room for one buffer. */
50	if (virtqueue_add_buf(vq, &sg, 0, 1, buf, GFP_KERNEL) < 0)
51		BUG();
52
53	virtqueue_kick(vq);
54}
55
56static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
57{
58
59	if (!busy) {
60		busy = true;
61		init_completion(&have_data);
62		register_buffer(buf, size);
63	}
64
65	if (!wait)
66		return 0;
67
68	wait_for_completion(&have_data);
69
70	busy = false;
71
72	return data_avail;
73}
74
75static void virtio_cleanup(struct hwrng *rng)
76{
77	if (busy)
78		wait_for_completion(&have_data);
79}
80
81
82static struct hwrng virtio_hwrng = {
83	.name		= "virtio",
84	.cleanup	= virtio_cleanup,
85	.read		= virtio_read,
86};
87
88static int virtrng_probe(struct virtio_device *vdev)
89{
90	int err;
91
92	/* We expect a single virtqueue. */
93	vq = virtio_find_single_vq(vdev, random_recv_done, "input");
94	if (IS_ERR(vq))
95		return PTR_ERR(vq);
96
97	err = hwrng_register(&virtio_hwrng);
98	if (err) {
99		vdev->config->del_vqs(vdev);
100		return err;
101	}
102
103	return 0;
104}
105
106static void __devexit virtrng_remove(struct virtio_device *vdev)
107{
108	vdev->config->reset(vdev);
109	hwrng_unregister(&virtio_hwrng);
110	vdev->config->del_vqs(vdev);
111}
112
113static struct virtio_device_id id_table[] = {
114	{ VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
115	{ 0 },
116};
117
118static struct virtio_driver virtio_rng_driver = {
119	.driver.name =	KBUILD_MODNAME,
120	.driver.owner =	THIS_MODULE,
121	.id_table =	id_table,
122	.probe =	virtrng_probe,
123	.remove =	__devexit_p(virtrng_remove),
124};
125
126static int __init init(void)
127{
128	return register_virtio_driver(&virtio_rng_driver);
129}
130
131static void __exit fini(void)
132{
133	unregister_virtio_driver(&virtio_rng_driver);
134}
135module_init(init);
136module_exit(fini);
137
138MODULE_DEVICE_TABLE(virtio, id_table);
139MODULE_DESCRIPTION("Virtio random number driver");
140MODULE_LICENSE("GPL");
141