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/module.h>
24 #include <linux/kernel.h>
25 #include <linux/platform_device.h>
26 #include <linux/hw_random.h>
27 #include <linux/io.h>
28 #include <linux/timeriomem-rng.h>
29 #include <linux/jiffies.h>
30 #include <linux/sched.h>
31 #include <linux/timer.h>
32 #include <linux/completion.h>
33 
34 static struct timeriomem_rng_data *timeriomem_rng_data;
35 
36 static void timeriomem_rng_trigger(unsigned long);
37 static DEFINE_TIMER(timeriomem_rng_timer, timeriomem_rng_trigger, 0, 0);
38 
39 /*
40  * have data return 1, however return 0 if we have nothing
41  */
42 static int timeriomem_rng_data_present(struct hwrng *rng, int wait)
43 {
44 	if (rng->priv == 0)
45 		return 1;
46 
47 	if (!wait || timeriomem_rng_data->present)
48 		return timeriomem_rng_data->present;
49 
50 	wait_for_completion(&timeriomem_rng_data->completion);
51 
52 	return 1;
53 }
54 
55 static int timeriomem_rng_data_read(struct hwrng *rng, u32 *data)
56 {
57 	unsigned long cur;
58 	s32 delay;
59 
60 	*data = readl(timeriomem_rng_data->address);
61 
62 	if (rng->priv != 0) {
63 		cur = jiffies;
64 
65 		delay = cur - timeriomem_rng_timer.expires;
66 		delay = rng->priv - (delay % rng->priv);
67 
68 		timeriomem_rng_timer.expires = cur + delay;
69 		timeriomem_rng_data->present = 0;
70 
71 		init_completion(&timeriomem_rng_data->completion);
72 		add_timer(&timeriomem_rng_timer);
73 	}
74 
75 	return 4;
76 }
77 
78 static void timeriomem_rng_trigger(unsigned long dummy)
79 {
80 	timeriomem_rng_data->present = 1;
81 	complete(&timeriomem_rng_data->completion);
82 }
83 
84 static struct hwrng timeriomem_rng_ops = {
85 	.name		= "timeriomem",
86 	.data_present	= timeriomem_rng_data_present,
87 	.data_read	= timeriomem_rng_data_read,
88 	.priv		= 0,
89 };
90 
91 static int __devinit timeriomem_rng_probe(struct platform_device *pdev)
92 {
93 	struct resource *res;
94 	int ret;
95 
96 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
97 
98 	if (!res)
99 		return -ENOENT;
100 
101 	timeriomem_rng_data = pdev->dev.platform_data;
102 
103 	timeriomem_rng_data->address = ioremap(res->start,
104 						res->end - res->start + 1);
105 	if (!timeriomem_rng_data->address)
106 		return -EIO;
107 
108 	if (timeriomem_rng_data->period != 0
109 		&& usecs_to_jiffies(timeriomem_rng_data->period) > 0) {
110 		timeriomem_rng_timer.expires = jiffies;
111 
112 		timeriomem_rng_ops.priv = usecs_to_jiffies(
113 						timeriomem_rng_data->period);
114 	}
115 	timeriomem_rng_data->present = 1;
116 
117 	ret = hwrng_register(&timeriomem_rng_ops);
118 	if (ret)
119 		goto failed;
120 
121 	dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
122 			timeriomem_rng_data->address,
123 			timeriomem_rng_data->period);
124 
125 	return 0;
126 
127 failed:
128 	dev_err(&pdev->dev, "problem registering\n");
129 	iounmap(timeriomem_rng_data->address);
130 
131 	return ret;
132 }
133 
134 static int __devexit timeriomem_rng_remove(struct platform_device *pdev)
135 {
136 	del_timer_sync(&timeriomem_rng_timer);
137 	hwrng_unregister(&timeriomem_rng_ops);
138 
139 	iounmap(timeriomem_rng_data->address);
140 
141 	return 0;
142 }
143 
144 static struct platform_driver timeriomem_rng_driver = {
145 	.driver = {
146 		.name		= "timeriomem_rng",
147 		.owner		= THIS_MODULE,
148 	},
149 	.probe		= timeriomem_rng_probe,
150 	.remove		= __devexit_p(timeriomem_rng_remove),
151 };
152 
153 static int __init timeriomem_rng_init(void)
154 {
155 	return platform_driver_register(&timeriomem_rng_driver);
156 }
157 
158 static void __exit timeriomem_rng_exit(void)
159 {
160 	platform_driver_unregister(&timeriomem_rng_driver);
161 }
162 
163 module_init(timeriomem_rng_init);
164 module_exit(timeriomem_rng_exit);
165 
166 MODULE_LICENSE("GPL");
167 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
168 MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");
169