1/*
  2 * Copyright (c) 2015, Daniel Thompson
  3 *
  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.
  8 *
  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.
 13 */
 14
 15#include <linux/clk.h>
 16#include <linux/delay.h>
 17#include <linux/hw_random.h>
 18#include <linux/io.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/slab.h>
 25
 26#define RNG_CR 0x00
 27#define RNG_CR_RNGEN BIT(2)
 28
 29#define RNG_SR 0x04
 30#define RNG_SR_SEIS BIT(6)
 31#define RNG_SR_CEIS BIT(5)
 32#define RNG_SR_DRDY BIT(0)
 33
 34#define RNG_DR 0x08
 35
 36/*
 37 * It takes 40 cycles @ 48MHz to generate each random number (e.g. <1us).
 38 * At the time of writing STM32 parts max out at ~200MHz meaning a timeout
 39 * of 500 leaves us a very comfortable margin for error. The loop to which
 40 * the timeout applies takes at least 4 instructions per iteration so the
 41 * timeout is enough to take us up to multi-GHz parts!
 42 */
 43#define RNG_TIMEOUT 500
 44
 45struct stm32_rng_private {
 46	struct hwrng rng;
 47	void __iomem *base;
 48	struct clk *clk;
 49};
 50
 51static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 52{
 53	struct stm32_rng_private *priv =
 54	    container_of(rng, struct stm32_rng_private, rng);
 55	u32 sr;
 56	int retval = 0;
 57
 58	pm_runtime_get_sync((struct device *) priv->rng.priv);
 59
 60	while (max > sizeof(u32)) {
 61		sr = readl_relaxed(priv->base + RNG_SR);
 62		if (!sr && wait) {
 63			unsigned int timeout = RNG_TIMEOUT;
 64
 65			do {
 66				cpu_relax();
 67				sr = readl_relaxed(priv->base + RNG_SR);
 68			} while (!sr && --timeout);
 69		}
 70
 71		/* If error detected or data not ready... */
 72		if (sr != RNG_SR_DRDY) {
 73			if (WARN_ONCE(sr & (RNG_SR_SEIS | RNG_SR_CEIS),
 74					"bad RNG status - %x\n", sr))
 75				writel_relaxed(0, priv->base + RNG_SR);
 76			break;
 77		}
 78
 79		*(u32 *)data = readl_relaxed(priv->base + RNG_DR);
 80
 81		retval += sizeof(u32);
 82		data += sizeof(u32);
 83		max -= sizeof(u32);
 84	}
 85
 86	pm_runtime_mark_last_busy((struct device *) priv->rng.priv);
 87	pm_runtime_put_sync_autosuspend((struct device *) priv->rng.priv);
 88
 89	return retval || !wait ? retval : -EIO;
 90}
 91
 92static int stm32_rng_init(struct hwrng *rng)
 93{
 94	struct stm32_rng_private *priv =
 95	    container_of(rng, struct stm32_rng_private, rng);
 96	int err;
 97
 98	err = clk_prepare_enable(priv->clk);
 99	if (err)
100		return err;
101
102	writel_relaxed(RNG_CR_RNGEN, priv->base + RNG_CR);
103
104	/* clear error indicators */
105	writel_relaxed(0, priv->base + RNG_SR);
106
107	return 0;
108}
109
110static void stm32_rng_cleanup(struct hwrng *rng)
111{
112	struct stm32_rng_private *priv =
113	    container_of(rng, struct stm32_rng_private, rng);
114
115	writel_relaxed(0, priv->base + RNG_CR);
116	clk_disable_unprepare(priv->clk);
117}
118
119static int stm32_rng_probe(struct platform_device *ofdev)
120{
121	struct device *dev = &ofdev->dev;
122	struct device_node *np = ofdev->dev.of_node;
123	struct stm32_rng_private *priv;
124	struct resource res;
125	int err;
126
127	priv = devm_kzalloc(dev, sizeof(struct stm32_rng_private), GFP_KERNEL);
128	if (!priv)
129		return -ENOMEM;
130
131	err = of_address_to_resource(np, 0, &res);
132	if (err)
133		return err;
134
135	priv->base = devm_ioremap_resource(dev, &res);
136	if (IS_ERR(priv->base))
137		return PTR_ERR(priv->base);
138
139	priv->clk = devm_clk_get(&ofdev->dev, NULL);
140	if (IS_ERR(priv->clk))
141		return PTR_ERR(priv->clk);
142
143	dev_set_drvdata(dev, priv);
144
145	priv->rng.name = dev_driver_string(dev),
146#ifndef CONFIG_PM
147	priv->rng.init = stm32_rng_init,
148	priv->rng.cleanup = stm32_rng_cleanup,
149#endif
150	priv->rng.read = stm32_rng_read,
151	priv->rng.priv = (unsigned long) dev;
152
153	pm_runtime_set_autosuspend_delay(dev, 100);
154	pm_runtime_use_autosuspend(dev);
155	pm_runtime_enable(dev);
156
157	return devm_hwrng_register(dev, &priv->rng);
158}
159
160#ifdef CONFIG_PM
161static int stm32_rng_runtime_suspend(struct device *dev)
162{
163	struct stm32_rng_private *priv = dev_get_drvdata(dev);
164
165	stm32_rng_cleanup(&priv->rng);
166
167	return 0;
168}
169
170static int stm32_rng_runtime_resume(struct device *dev)
171{
172	struct stm32_rng_private *priv = dev_get_drvdata(dev);
173
174	return stm32_rng_init(&priv->rng);
175}
176#endif
177
178static UNIVERSAL_DEV_PM_OPS(stm32_rng_pm_ops, stm32_rng_runtime_suspend,
179			    stm32_rng_runtime_resume, NULL);
180
181static const struct of_device_id stm32_rng_match[] = {
182	{
183		.compatible = "st,stm32-rng",
184	},
185	{},
186};
187MODULE_DEVICE_TABLE(of, stm32_rng_match);
188
189static struct platform_driver stm32_rng_driver = {
190	.driver = {
191		.name = "stm32-rng",
192		.pm = &stm32_rng_pm_ops,
193		.of_match_table = stm32_rng_match,
194	},
195	.probe = stm32_rng_probe,
196};
197
198module_platform_driver(stm32_rng_driver);
199
200MODULE_LICENSE("GPL");
201MODULE_AUTHOR("Daniel Thompson <daniel.thompson@linaro.org>");
202MODULE_DESCRIPTION("STMicroelectronics STM32 RNG device driver");