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
33struct 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
44static 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
92static 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
103static 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
177static 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
186static const struct of_device_id timeriomem_rng_match[] = {
187	{ .compatible = "timeriomem_rng" },
188	{},
189};
190MODULE_DEVICE_TABLE(of, timeriomem_rng_match);
191
192static 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
201module_platform_driver(timeriomem_rng_driver);
202
203MODULE_LICENSE("GPL");
204MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
205MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");
206