2 * Copyright (c) 2015, Daniel Thompson
4 * This file is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; either version 2
7 * of the License, or (at your option) any later version.
9 * This file is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
15 #include <linux/clk.h>
16 #include <linux/delay.h>
17 #include <linux/hw_random.h>
19 #include <linux/kernel.h>
20 #include <linux/module.h>
21 #include <linux/of_address.h>
22 #include <linux/of_platform.h>
23 #include <linux/pm_runtime.h>
24 #include <linux/reset.h>
25 #include <linux/slab.h>
28 #define RNG_CR_RNGEN BIT(2)
31 #define RNG_SR_SEIS BIT(6)
32 #define RNG_SR_CEIS BIT(5)
33 #define RNG_SR_DRDY BIT(0)
38 * It takes 40 cycles @ 48MHz to generate each random number (e.g. <1us).
39 * At the time of writing STM32 parts max out at ~200MHz meaning a timeout
40 * of 500 leaves us a very comfortable margin for error. The loop to which
41 * the timeout applies takes at least 4 instructions per iteration so the
42 * timeout is enough to take us up to multi-GHz parts!
44 #define RNG_TIMEOUT 500
46 struct stm32_rng_private {
50 struct reset_control *rst;
53 static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
55 struct stm32_rng_private *priv =
56 container_of(rng, struct stm32_rng_private, rng);
60 pm_runtime_get_sync((struct device *) priv->rng.priv);
62 while (max > sizeof(u32)) {
63 sr = readl_relaxed(priv->base + RNG_SR);
65 unsigned int timeout = RNG_TIMEOUT;
69 sr = readl_relaxed(priv->base + RNG_SR);
70 } while (!sr && --timeout);
73 /* If error detected or data not ready... */
74 if (sr != RNG_SR_DRDY)
77 *(u32 *)data = readl_relaxed(priv->base + RNG_DR);
79 retval += sizeof(u32);
84 if (WARN_ONCE(sr & (RNG_SR_SEIS | RNG_SR_CEIS),
85 "bad RNG status - %x\n", sr))
86 writel_relaxed(0, priv->base + RNG_SR);
88 pm_runtime_mark_last_busy((struct device *) priv->rng.priv);
89 pm_runtime_put_sync_autosuspend((struct device *) priv->rng.priv);
91 return retval || !wait ? retval : -EIO;
94 static int stm32_rng_init(struct hwrng *rng)
96 struct stm32_rng_private *priv =
97 container_of(rng, struct stm32_rng_private, rng);
100 err = clk_prepare_enable(priv->clk);
104 writel_relaxed(RNG_CR_RNGEN, priv->base + RNG_CR);
106 /* clear error indicators */
107 writel_relaxed(0, priv->base + RNG_SR);
112 static void stm32_rng_cleanup(struct hwrng *rng)
114 struct stm32_rng_private *priv =
115 container_of(rng, struct stm32_rng_private, rng);
117 writel_relaxed(0, priv->base + RNG_CR);
118 clk_disable_unprepare(priv->clk);
121 static int stm32_rng_probe(struct platform_device *ofdev)
123 struct device *dev = &ofdev->dev;
124 struct device_node *np = ofdev->dev.of_node;
125 struct stm32_rng_private *priv;
129 priv = devm_kzalloc(dev, sizeof(struct stm32_rng_private), GFP_KERNEL);
133 err = of_address_to_resource(np, 0, &res);
137 priv->base = devm_ioremap_resource(dev, &res);
138 if (IS_ERR(priv->base))
139 return PTR_ERR(priv->base);
141 priv->clk = devm_clk_get(&ofdev->dev, NULL);
142 if (IS_ERR(priv->clk))
143 return PTR_ERR(priv->clk);
145 priv->rst = devm_reset_control_get(&ofdev->dev, NULL);
146 if (!IS_ERR(priv->rst)) {
147 reset_control_assert(priv->rst);
149 reset_control_deassert(priv->rst);
152 dev_set_drvdata(dev, priv);
154 priv->rng.name = dev_driver_string(dev),
156 priv->rng.init = stm32_rng_init,
157 priv->rng.cleanup = stm32_rng_cleanup,
159 priv->rng.read = stm32_rng_read,
160 priv->rng.priv = (unsigned long) dev;
162 pm_runtime_set_autosuspend_delay(dev, 100);
163 pm_runtime_use_autosuspend(dev);
164 pm_runtime_enable(dev);
166 return devm_hwrng_register(dev, &priv->rng);
169 static int stm32_rng_remove(struct platform_device *ofdev)
171 pm_runtime_disable(&ofdev->dev);
177 static int stm32_rng_runtime_suspend(struct device *dev)
179 struct stm32_rng_private *priv = dev_get_drvdata(dev);
181 stm32_rng_cleanup(&priv->rng);
186 static int stm32_rng_runtime_resume(struct device *dev)
188 struct stm32_rng_private *priv = dev_get_drvdata(dev);
190 return stm32_rng_init(&priv->rng);
194 static UNIVERSAL_DEV_PM_OPS(stm32_rng_pm_ops, stm32_rng_runtime_suspend,
195 stm32_rng_runtime_resume, NULL);
197 static const struct of_device_id stm32_rng_match[] = {
199 .compatible = "st,stm32-rng",
203 MODULE_DEVICE_TABLE(of, stm32_rng_match);
205 static struct platform_driver stm32_rng_driver = {
208 .pm = &stm32_rng_pm_ops,
209 .of_match_table = stm32_rng_match,
211 .probe = stm32_rng_probe,
212 .remove = stm32_rng_remove,
215 module_platform_driver(stm32_rng_driver);
217 MODULE_LICENSE("GPL");
218 MODULE_AUTHOR("Daniel Thompson <daniel.thompson@linaro.org>");
219 MODULE_DESCRIPTION("STMicroelectronics STM32 RNG device driver");