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 
45 struct stm32_rng_private {
46 	struct hwrng rng;
47 	void __iomem *base;
48 	struct clk *clk;
49 };
50 
51 static 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 
92 static 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 
110 static 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 
119 static 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
161 static 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 
170 static 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 
178 static UNIVERSAL_DEV_PM_OPS(stm32_rng_pm_ops, stm32_rng_runtime_suspend,
179 			    stm32_rng_runtime_resume, NULL);
180 
181 static const struct of_device_id stm32_rng_match[] = {
182 	{
183 		.compatible = "st,stm32-rng",
184 	},
185 	{},
186 };
187 MODULE_DEVICE_TABLE(of, stm32_rng_match);
188 
189 static 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 
198 module_platform_driver(stm32_rng_driver);
199 
200 MODULE_LICENSE("GPL");
201 MODULE_AUTHOR("Daniel Thompson <daniel.thompson@linaro.org>");
202 MODULE_DESCRIPTION("STMicroelectronics STM32 RNG device driver");
203