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 
28 static struct virtqueue *vq;
29 static unsigned int data_avail;
30 static DECLARE_COMPLETION(have_data);
31 static bool busy;
32 
33 static 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. */
43 static 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 	virtqueue_add_inbuf(vq, &sg, 1, buf, GFP_KERNEL);
51 
52 	virtqueue_kick(vq);
53 }
54 
55 static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
56 {
57 	int ret;
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 	ret = wait_for_completion_killable(&have_data);
69 	if (ret < 0)
70 		return ret;
71 
72 	busy = false;
73 
74 	return data_avail;
75 }
76 
77 static void virtio_cleanup(struct hwrng *rng)
78 {
79 	if (busy)
80 		wait_for_completion(&have_data);
81 }
82 
83 
84 static struct hwrng virtio_hwrng = {
85 	.name		= "virtio",
86 	.cleanup	= virtio_cleanup,
87 	.read		= virtio_read,
88 };
89 
90 static int probe_common(struct virtio_device *vdev)
91 {
92 	int err;
93 
94 	if (vq) {
95 		/* We only support one device for now */
96 		return -EBUSY;
97 	}
98 	/* We expect a single virtqueue. */
99 	vq = virtio_find_single_vq(vdev, random_recv_done, "input");
100 	if (IS_ERR(vq)) {
101 		err = PTR_ERR(vq);
102 		vq = NULL;
103 		return err;
104 	}
105 
106 	err = hwrng_register(&virtio_hwrng);
107 	if (err) {
108 		vdev->config->del_vqs(vdev);
109 		vq = NULL;
110 		return err;
111 	}
112 
113 	return 0;
114 }
115 
116 static void remove_common(struct virtio_device *vdev)
117 {
118 	vdev->config->reset(vdev);
119 	busy = false;
120 	hwrng_unregister(&virtio_hwrng);
121 	vdev->config->del_vqs(vdev);
122 	vq = NULL;
123 }
124 
125 static int virtrng_probe(struct virtio_device *vdev)
126 {
127 	return probe_common(vdev);
128 }
129 
130 static void virtrng_remove(struct virtio_device *vdev)
131 {
132 	remove_common(vdev);
133 }
134 
135 #ifdef CONFIG_PM_SLEEP
136 static int virtrng_freeze(struct virtio_device *vdev)
137 {
138 	remove_common(vdev);
139 	return 0;
140 }
141 
142 static int virtrng_restore(struct virtio_device *vdev)
143 {
144 	return probe_common(vdev);
145 }
146 #endif
147 
148 static struct virtio_device_id id_table[] = {
149 	{ VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
150 	{ 0 },
151 };
152 
153 static struct virtio_driver virtio_rng_driver = {
154 	.driver.name =	KBUILD_MODNAME,
155 	.driver.owner =	THIS_MODULE,
156 	.id_table =	id_table,
157 	.probe =	virtrng_probe,
158 	.remove =	virtrng_remove,
159 #ifdef CONFIG_PM_SLEEP
160 	.freeze =	virtrng_freeze,
161 	.restore =	virtrng_restore,
162 #endif
163 };
164 
165 module_virtio_driver(virtio_rng_driver);
166 MODULE_DEVICE_TABLE(virtio, id_table);
167 MODULE_DESCRIPTION("Virtio random number driver");
168 MODULE_LICENSE("GPL");
169