1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * drivers/char/hw_random/timeriomem-rng.c
4 *
5 * Copyright (C) 2009 Alexander Clouter <alex@digriz.org.uk>
6 *
7 * Derived from drivers/char/hw_random/omap-rng.c
8 * Copyright 2005 (c) MontaVista Software, Inc.
9 * Author: Deepak Saxena <dsaxena@plexity.net>
10 *
11 * Overview:
12 * This driver is useful for platforms that have an IO range that provides
13 * periodic random data from a single IO memory address. All the platform
14 * has to do is provide the address and 'wait time' that new data becomes
15 * available.
16 *
17 * TODO: add support for reading sizes other than 32bits and masking
18 */
19
20 #include <linux/completion.h>
21 #include <linux/delay.h>
22 #include <linux/hrtimer.h>
23 #include <linux/hw_random.h>
24 #include <linux/io.h>
25 #include <linux/ktime.h>
26 #include <linux/module.h>
27 #include <linux/of.h>
28 #include <linux/platform_device.h>
29 #include <linux/slab.h>
30 #include <linux/time.h>
31 #include <linux/timeriomem-rng.h>
32
33 struct timeriomem_rng_private {
34 void __iomem *io_base;
35 ktime_t period;
36 unsigned int present:1;
37
38 struct hrtimer timer;
39 struct completion completion;
40
41 struct hwrng rng_ops;
42 };
43
timeriomem_rng_read(struct hwrng * hwrng,void * data,size_t max,bool wait)44 static int timeriomem_rng_read(struct hwrng *hwrng, void *data,
45 size_t max, bool wait)
46 {
47 struct timeriomem_rng_private *priv =
48 container_of(hwrng, struct timeriomem_rng_private, rng_ops);
49 int retval = 0;
50 int period_us = ktime_to_us(priv->period);
51
52 /*
53 * There may not have been enough time for new data to be generated
54 * since the last request. If the caller doesn't want to wait, let them
55 * bail out. Otherwise, wait for the completion. If the new data has
56 * already been generated, the completion should already be available.
57 */
58 if (!wait && !priv->present)
59 return 0;
60
61 wait_for_completion(&priv->completion);
62
63 do {
64 /*
65 * After the first read, all additional reads will need to wait
66 * for the RNG to generate new data. Since the period can have
67 * a wide range of values (1us to 1s have been observed), allow
68 * for 1% tolerance in the sleep time rather than a fixed value.
69 */
70 if (retval > 0)
71 usleep_range(period_us,
72 period_us + max(1, period_us / 100));
73
74 *(u32 *)data = readl(priv->io_base);
75 retval += sizeof(u32);
76 data += sizeof(u32);
77 max -= sizeof(u32);
78 } while (wait && max > sizeof(u32));
79
80 /*
81 * Block any new callers until the RNG has had time to generate new
82 * data.
83 */
84 priv->present = 0;
85 reinit_completion(&priv->completion);
86 hrtimer_forward_now(&priv->timer, priv->period);
87 hrtimer_restart(&priv->timer);
88
89 return retval;
90 }
91
timeriomem_rng_trigger(struct hrtimer * timer)92 static enum hrtimer_restart timeriomem_rng_trigger(struct hrtimer *timer)
93 {
94 struct timeriomem_rng_private *priv
95 = container_of(timer, struct timeriomem_rng_private, timer);
96
97 priv->present = 1;
98 complete(&priv->completion);
99
100 return HRTIMER_NORESTART;
101 }
102
timeriomem_rng_probe(struct platform_device * pdev)103 static int timeriomem_rng_probe(struct platform_device *pdev)
104 {
105 struct timeriomem_rng_data *pdata = pdev->dev.platform_data;
106 struct timeriomem_rng_private *priv;
107 struct resource *res;
108 int err = 0;
109 int period;
110
111 if (!pdev->dev.of_node && !pdata) {
112 dev_err(&pdev->dev, "timeriomem_rng_data is missing\n");
113 return -EINVAL;
114 }
115
116 /* Allocate memory for the device structure (and zero it) */
117 priv = devm_kzalloc(&pdev->dev,
118 sizeof(struct timeriomem_rng_private), GFP_KERNEL);
119 if (!priv)
120 return -ENOMEM;
121
122 platform_set_drvdata(pdev, priv);
123
124 priv->io_base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
125 if (IS_ERR(priv->io_base))
126 return PTR_ERR(priv->io_base);
127
128 if (res->start % 4 != 0 || resource_size(res) < 4) {
129 dev_err(&pdev->dev,
130 "address must be at least four bytes wide and 32-bit aligned\n");
131 return -EINVAL;
132 }
133
134 if (pdev->dev.of_node) {
135 int i;
136
137 if (!of_property_read_u32(pdev->dev.of_node,
138 "period", &i))
139 period = i;
140 else {
141 dev_err(&pdev->dev, "missing period\n");
142 return -EINVAL;
143 }
144
145 if (!of_property_read_u32(pdev->dev.of_node,
146 "quality", &i))
147 priv->rng_ops.quality = i;
148 } else {
149 period = pdata->period;
150 priv->rng_ops.quality = pdata->quality;
151 }
152
153 priv->period = ns_to_ktime(period * NSEC_PER_USEC);
154 init_completion(&priv->completion);
155 hrtimer_init(&priv->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
156 priv->timer.function = timeriomem_rng_trigger;
157
158 priv->rng_ops.name = dev_name(&pdev->dev);
159 priv->rng_ops.read = timeriomem_rng_read;
160
161 /* Assume random data is already available. */
162 priv->present = 1;
163 complete(&priv->completion);
164
165 err = devm_hwrng_register(&pdev->dev, &priv->rng_ops);
166 if (err) {
167 dev_err(&pdev->dev, "problem registering\n");
168 return err;
169 }
170
171 dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
172 priv->io_base, period);
173
174 return 0;
175 }
176
timeriomem_rng_remove(struct platform_device * pdev)177 static int timeriomem_rng_remove(struct platform_device *pdev)
178 {
179 struct timeriomem_rng_private *priv = platform_get_drvdata(pdev);
180
181 hrtimer_cancel(&priv->timer);
182
183 return 0;
184 }
185
186 static const struct of_device_id timeriomem_rng_match[] = {
187 { .compatible = "timeriomem_rng" },
188 {},
189 };
190 MODULE_DEVICE_TABLE(of, timeriomem_rng_match);
191
192 static struct platform_driver timeriomem_rng_driver = {
193 .driver = {
194 .name = "timeriomem_rng",
195 .of_match_table = timeriomem_rng_match,
196 },
197 .probe = timeriomem_rng_probe,
198 .remove = timeriomem_rng_remove,
199 };
200
201 module_platform_driver(timeriomem_rng_driver);
202
203 MODULE_LICENSE("GPL");
204 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
205 MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");
206