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/of.h>
27 #include <linux/hw_random.h>
28 #include <linux/io.h>
29 #include <linux/slab.h>
30 #include <linux/timeriomem-rng.h>
31 #include <linux/jiffies.h>
32 #include <linux/sched.h>
33 #include <linux/timer.h>
34 #include <linux/completion.h>
35 
36 struct timeriomem_rng_private_data {
37 	void __iomem		*io_base;
38 	unsigned int		expires;
39 	unsigned int		period;
40 	unsigned int		present:1;
41 
42 	struct timer_list	timer;
43 	struct completion	completion;
44 
45 	struct hwrng		timeriomem_rng_ops;
46 };
47 
48 #define to_rng_priv(rng) \
49 		((struct timeriomem_rng_private_data *)rng->priv)
50 
51 /*
52  * have data return 1, however return 0 if we have nothing
53  */
54 static int timeriomem_rng_data_present(struct hwrng *rng, int wait)
55 {
56 	struct timeriomem_rng_private_data *priv = to_rng_priv(rng);
57 
58 	if (!wait || priv->present)
59 		return priv->present;
60 
61 	wait_for_completion(&priv->completion);
62 
63 	return 1;
64 }
65 
66 static int timeriomem_rng_data_read(struct hwrng *rng, u32 *data)
67 {
68 	struct timeriomem_rng_private_data *priv = to_rng_priv(rng);
69 	unsigned long cur;
70 	s32 delay;
71 
72 	*data = readl(priv->io_base);
73 
74 	cur = jiffies;
75 
76 	delay = cur - priv->expires;
77 	delay = priv->period - (delay % priv->period);
78 
79 	priv->expires = cur + delay;
80 	priv->present = 0;
81 
82 	reinit_completion(&priv->completion);
83 	mod_timer(&priv->timer, priv->expires);
84 
85 	return 4;
86 }
87 
88 static void timeriomem_rng_trigger(unsigned long data)
89 {
90 	struct timeriomem_rng_private_data *priv
91 			= (struct timeriomem_rng_private_data *)data;
92 
93 	priv->present = 1;
94 	complete(&priv->completion);
95 }
96 
97 static int timeriomem_rng_probe(struct platform_device *pdev)
98 {
99 	struct timeriomem_rng_data *pdata = pdev->dev.platform_data;
100 	struct timeriomem_rng_private_data *priv;
101 	struct resource *res;
102 	int err = 0;
103 	int period;
104 
105 	if (!pdev->dev.of_node && !pdata) {
106 		dev_err(&pdev->dev, "timeriomem_rng_data is missing\n");
107 		return -EINVAL;
108 	}
109 
110 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
111 	if (!res)
112 		return -ENXIO;
113 
114 	if (res->start % 4 != 0 || resource_size(res) != 4) {
115 		dev_err(&pdev->dev,
116 			"address must be four bytes wide and aligned\n");
117 		return -EINVAL;
118 	}
119 
120 	/* Allocate memory for the device structure (and zero it) */
121 	priv = devm_kzalloc(&pdev->dev,
122 			sizeof(struct timeriomem_rng_private_data), GFP_KERNEL);
123 	if (!priv)
124 		return -ENOMEM;
125 
126 	platform_set_drvdata(pdev, priv);
127 
128 	if (pdev->dev.of_node) {
129 		int i;
130 
131 		if (!of_property_read_u32(pdev->dev.of_node,
132 						"period", &i))
133 			period = i;
134 		else {
135 			dev_err(&pdev->dev, "missing period\n");
136 			return -EINVAL;
137 		}
138 	} else {
139 		period = pdata->period;
140 	}
141 
142 	priv->period = usecs_to_jiffies(period);
143 	if (priv->period < 1) {
144 		dev_err(&pdev->dev, "period is less than one jiffy\n");
145 		return -EINVAL;
146 	}
147 
148 	priv->expires	= jiffies;
149 	priv->present	= 1;
150 
151 	init_completion(&priv->completion);
152 	complete(&priv->completion);
153 
154 	setup_timer(&priv->timer, timeriomem_rng_trigger, (unsigned long)priv);
155 
156 	priv->timeriomem_rng_ops.name		= dev_name(&pdev->dev);
157 	priv->timeriomem_rng_ops.data_present	= timeriomem_rng_data_present;
158 	priv->timeriomem_rng_ops.data_read	= timeriomem_rng_data_read;
159 	priv->timeriomem_rng_ops.priv		= (unsigned long)priv;
160 
161 	priv->io_base = devm_ioremap_resource(&pdev->dev, res);
162 	if (IS_ERR(priv->io_base)) {
163 		err = PTR_ERR(priv->io_base);
164 		goto out_timer;
165 	}
166 
167 	err = hwrng_register(&priv->timeriomem_rng_ops);
168 	if (err) {
169 		dev_err(&pdev->dev, "problem registering\n");
170 		goto out_timer;
171 	}
172 
173 	dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
174 			priv->io_base, period);
175 
176 	return 0;
177 
178 out_timer:
179 	del_timer_sync(&priv->timer);
180 	return err;
181 }
182 
183 static int timeriomem_rng_remove(struct platform_device *pdev)
184 {
185 	struct timeriomem_rng_private_data *priv = platform_get_drvdata(pdev);
186 
187 	hwrng_unregister(&priv->timeriomem_rng_ops);
188 
189 	del_timer_sync(&priv->timer);
190 
191 	return 0;
192 }
193 
194 static const struct of_device_id timeriomem_rng_match[] = {
195 	{ .compatible = "timeriomem_rng" },
196 	{},
197 };
198 MODULE_DEVICE_TABLE(of, timeriomem_rng_match);
199 
200 static struct platform_driver timeriomem_rng_driver = {
201 	.driver = {
202 		.name		= "timeriomem_rng",
203 		.of_match_table	= timeriomem_rng_match,
204 	},
205 	.probe		= timeriomem_rng_probe,
206 	.remove		= timeriomem_rng_remove,
207 };
208 
209 module_platform_driver(timeriomem_rng_driver);
210 
211 MODULE_LICENSE("GPL");
212 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
213 MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");
214