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 
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 
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 
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 
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