1 // SPDX-License-Identifier: GPL-2.0-only
3 * drivers/char/hw_random/timeriomem-rng.c
5 * Copyright (C) 2009 Alexander Clouter <alex@digriz.org.uk>
7 * Derived from drivers/char/hw_random/omap-rng.c
8 * Copyright 2005 (c) MontaVista Software, Inc.
9 * Author: Deepak Saxena <dsaxena@plexity.net>
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
17 * TODO: add support for reading sizes other than 32bits and masking
20 #include <linux/completion.h>
21 #include <linux/delay.h>
22 #include <linux/hrtimer.h>
23 #include <linux/hw_random.h>
25 #include <linux/ktime.h>
26 #include <linux/module.h>
28 #include <linux/platform_device.h>
29 #include <linux/slab.h>
30 #include <linux/time.h>
31 #include <linux/timeriomem-rng.h>
33 struct timeriomem_rng_private {
34 void __iomem *io_base;
36 unsigned int present:1;
39 struct completion completion;
44 static int timeriomem_rng_read(struct hwrng *hwrng, void *data,
45 size_t max, bool wait)
47 struct timeriomem_rng_private *priv =
48 container_of(hwrng, struct timeriomem_rng_private, rng_ops);
50 int period_us = ktime_to_us(priv->period);
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.
58 if (!wait && !priv->present)
61 wait_for_completion(&priv->completion);
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.
71 usleep_range(period_us,
72 period_us + min(1, period_us / 100));
74 *(u32 *)data = readl(priv->io_base);
75 retval += sizeof(u32);
78 } while (wait && max > sizeof(u32));
81 * Block any new callers until the RNG has had time to generate new
85 reinit_completion(&priv->completion);
86 hrtimer_forward_now(&priv->timer, priv->period);
87 hrtimer_restart(&priv->timer);
92 static enum hrtimer_restart timeriomem_rng_trigger(struct hrtimer *timer)
94 struct timeriomem_rng_private *priv
95 = container_of(timer, struct timeriomem_rng_private, timer);
98 complete(&priv->completion);
100 return HRTIMER_NORESTART;
103 static int timeriomem_rng_probe(struct platform_device *pdev)
105 struct timeriomem_rng_data *pdata = pdev->dev.platform_data;
106 struct timeriomem_rng_private *priv;
107 struct resource *res;
111 if (!pdev->dev.of_node && !pdata) {
112 dev_err(&pdev->dev, "timeriomem_rng_data is missing\n");
116 res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
120 if (res->start % 4 != 0 || resource_size(res) < 4) {
122 "address must be at least four bytes wide and 32-bit aligned\n");
126 /* Allocate memory for the device structure (and zero it) */
127 priv = devm_kzalloc(&pdev->dev,
128 sizeof(struct timeriomem_rng_private), GFP_KERNEL);
132 platform_set_drvdata(pdev, priv);
134 if (pdev->dev.of_node) {
137 if (!of_property_read_u32(pdev->dev.of_node,
141 dev_err(&pdev->dev, "missing period\n");
145 if (!of_property_read_u32(pdev->dev.of_node,
147 priv->rng_ops.quality = i;
149 priv->rng_ops.quality = 0;
151 period = pdata->period;
152 priv->rng_ops.quality = pdata->quality;
155 priv->period = ns_to_ktime(period * NSEC_PER_USEC);
156 init_completion(&priv->completion);
157 hrtimer_init(&priv->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
158 priv->timer.function = timeriomem_rng_trigger;
160 priv->rng_ops.name = dev_name(&pdev->dev);
161 priv->rng_ops.read = timeriomem_rng_read;
163 priv->io_base = devm_ioremap_resource(&pdev->dev, res);
164 if (IS_ERR(priv->io_base)) {
165 return PTR_ERR(priv->io_base);
168 /* Assume random data is already available. */
170 complete(&priv->completion);
172 err = hwrng_register(&priv->rng_ops);
174 dev_err(&pdev->dev, "problem registering\n");
178 dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
179 priv->io_base, period);
184 static int timeriomem_rng_remove(struct platform_device *pdev)
186 struct timeriomem_rng_private *priv = platform_get_drvdata(pdev);
188 hwrng_unregister(&priv->rng_ops);
189 hrtimer_cancel(&priv->timer);
194 static const struct of_device_id timeriomem_rng_match[] = {
195 { .compatible = "timeriomem_rng" },
198 MODULE_DEVICE_TABLE(of, timeriomem_rng_match);
200 static struct platform_driver timeriomem_rng_driver = {
202 .name = "timeriomem_rng",
203 .of_match_table = timeriomem_rng_match,
205 .probe = timeriomem_rng_probe,
206 .remove = timeriomem_rng_remove,
209 module_platform_driver(timeriomem_rng_driver);
211 MODULE_LICENSE("GPL");
212 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
213 MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");