1 /*
2 * drivers/char/hw_random/timeriomem-rng.c
3 *
4 * Copyright (C) 2009 Alexander Clouter <alex@digriz.org.uk>
5 *
6 * Derived from drivers/char/hw_random/omap-rng.c
7 * Copyright 2005 (c) MontaVista Software, Inc.
8 * Author: Deepak Saxena <dsaxena@plexity.net>
9 *
10 * This program is free software; you can redistribute it and/or modify
11 * it under the terms of the GNU General Public License version 2 as
12 * published by the Free Software Foundation.
13 *
14 * Overview:
15 * This driver is useful for platforms that have an IO range that provides
16 * periodic random data from a single IO memory address. All the platform
17 * has to do is provide the address and 'wait time' that new data becomes
18 * available.
19 *
20 * TODO: add support for reading sizes other than 32bits and masking
21 */
22
23 #include <linux/completion.h>
24 #include <linux/delay.h>
25 #include <linux/hrtimer.h>
26 #include <linux/hw_random.h>
27 #include <linux/io.h>
28 #include <linux/ktime.h>
29 #include <linux/module.h>
30 #include <linux/of.h>
31 #include <linux/platform_device.h>
32 #include <linux/slab.h>
33 #include <linux/time.h>
34 #include <linux/timeriomem-rng.h>
35
36 struct timeriomem_rng_private {
37 void __iomem *io_base;
38 ktime_t period;
39 unsigned int present:1;
40
41 struct hrtimer timer;
42 struct completion completion;
43
44 struct hwrng rng_ops;
45 };
46
timeriomem_rng_read(struct hwrng * hwrng,void * data,size_t max,bool wait)47 static int timeriomem_rng_read(struct hwrng *hwrng, void *data,
48 size_t max, bool wait)
49 {
50 struct timeriomem_rng_private *priv =
51 container_of(hwrng, struct timeriomem_rng_private, rng_ops);
52 int retval = 0;
53 int period_us = ktime_to_us(priv->period);
54
55 /*
56 * The RNG provides 32-bits per read. Ensure there is enough space for
57 * at minimum one read.
58 */
59 if (max < sizeof(u32))
60 return 0;
61
62 /*
63 * There may not have been enough time for new data to be generated
64 * since the last request. If the caller doesn't want to wait, let them
65 * bail out. Otherwise, wait for the completion. If the new data has
66 * already been generated, the completion should already be available.
67 */
68 if (!wait && !priv->present)
69 return 0;
70
71 wait_for_completion(&priv->completion);
72
73 do {
74 /*
75 * After the first read, all additional reads will need to wait
76 * for the RNG to generate new data. Since the period can have
77 * a wide range of values (1us to 1s have been observed), allow
78 * for 1% tolerance in the sleep time rather than a fixed value.
79 */
80 if (retval > 0)
81 usleep_range(period_us,
82 period_us + min(1, period_us / 100));
83
84 *(u32 *)data = readl(priv->io_base);
85 retval += sizeof(u32);
86 data += sizeof(u32);
87 max -= sizeof(u32);
88 } while (wait && max > sizeof(u32));
89
90 /*
91 * Block any new callers until the RNG has had time to generate new
92 * data.
93 */
94 priv->present = 0;
95 reinit_completion(&priv->completion);
96 hrtimer_forward_now(&priv->timer, priv->period);
97 hrtimer_restart(&priv->timer);
98
99 return retval;
100 }
101
timeriomem_rng_trigger(struct hrtimer * timer)102 static enum hrtimer_restart timeriomem_rng_trigger(struct hrtimer *timer)
103 {
104 struct timeriomem_rng_private *priv
105 = container_of(timer, struct timeriomem_rng_private, timer);
106
107 priv->present = 1;
108 complete(&priv->completion);
109
110 return HRTIMER_NORESTART;
111 }
112
timeriomem_rng_probe(struct platform_device * pdev)113 static int timeriomem_rng_probe(struct platform_device *pdev)
114 {
115 struct timeriomem_rng_data *pdata = pdev->dev.platform_data;
116 struct timeriomem_rng_private *priv;
117 struct resource *res;
118 int err = 0;
119 int period;
120
121 if (!pdev->dev.of_node && !pdata) {
122 dev_err(&pdev->dev, "timeriomem_rng_data is missing\n");
123 return -EINVAL;
124 }
125
126 res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
127 if (!res)
128 return -ENXIO;
129
130 if (res->start % 4 != 0 || resource_size(res) != 4) {
131 dev_err(&pdev->dev,
132 "address must be four bytes wide and aligned\n");
133 return -EINVAL;
134 }
135
136 /* Allocate memory for the device structure (and zero it) */
137 priv = devm_kzalloc(&pdev->dev,
138 sizeof(struct timeriomem_rng_private), GFP_KERNEL);
139 if (!priv)
140 return -ENOMEM;
141
142 platform_set_drvdata(pdev, priv);
143
144 if (pdev->dev.of_node) {
145 int i;
146
147 if (!of_property_read_u32(pdev->dev.of_node,
148 "period", &i))
149 period = i;
150 else {
151 dev_err(&pdev->dev, "missing period\n");
152 return -EINVAL;
153 }
154
155 if (!of_property_read_u32(pdev->dev.of_node,
156 "quality", &i))
157 priv->rng_ops.quality = i;
158 else
159 priv->rng_ops.quality = 0;
160 } else {
161 period = pdata->period;
162 priv->rng_ops.quality = pdata->quality;
163 }
164
165 priv->period = ns_to_ktime(period * NSEC_PER_USEC);
166 init_completion(&priv->completion);
167 hrtimer_init(&priv->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
168 priv->timer.function = timeriomem_rng_trigger;
169
170 priv->rng_ops.name = dev_name(&pdev->dev);
171 priv->rng_ops.read = timeriomem_rng_read;
172
173 priv->io_base = devm_ioremap_resource(&pdev->dev, res);
174 if (IS_ERR(priv->io_base)) {
175 return PTR_ERR(priv->io_base);
176 }
177
178 /* Assume random data is already available. */
179 priv->present = 1;
180 complete(&priv->completion);
181
182 err = hwrng_register(&priv->rng_ops);
183 if (err) {
184 dev_err(&pdev->dev, "problem registering\n");
185 return err;
186 }
187
188 dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
189 priv->io_base, period);
190
191 return 0;
192 }
193
timeriomem_rng_remove(struct platform_device * pdev)194 static int timeriomem_rng_remove(struct platform_device *pdev)
195 {
196 struct timeriomem_rng_private *priv = platform_get_drvdata(pdev);
197
198 hwrng_unregister(&priv->rng_ops);
199 hrtimer_cancel(&priv->timer);
200
201 return 0;
202 }
203
204 static const struct of_device_id timeriomem_rng_match[] = {
205 { .compatible = "timeriomem_rng" },
206 {},
207 };
208 MODULE_DEVICE_TABLE(of, timeriomem_rng_match);
209
210 static struct platform_driver timeriomem_rng_driver = {
211 .driver = {
212 .name = "timeriomem_rng",
213 .of_match_table = timeriomem_rng_match,
214 },
215 .probe = timeriomem_rng_probe,
216 .remove = timeriomem_rng_remove,
217 };
218
219 module_platform_driver(timeriomem_rng_driver);
220
221 MODULE_LICENSE("GPL");
222 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
223 MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");
224