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 break; 74 75 *(u32 *)data = readl_relaxed(priv->base + RNG_DR); 76 77 retval += sizeof(u32); 78 data += sizeof(u32); 79 max -= sizeof(u32); 80 } 81 82 if (WARN_ONCE(sr & (RNG_SR_SEIS | RNG_SR_CEIS), 83 "bad RNG status - %x\n", sr)) 84 writel_relaxed(0, priv->base + RNG_SR); 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