drivers/char/hw_random/stm32-rng.c

   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/reset.h>
  25 #include <linux/slab.h>
  26
  27 #define RNG_CR 0x00
  28 #define RNG_CR_RNGEN BIT(2)
  29
  30 #define RNG_SR 0x04
  31 #define RNG_SR_SEIS BIT(6)
  32 #define RNG_SR_CEIS BIT(5)
  33 #define RNG_SR_DRDY BIT(0)
  34
  35 #define RNG_DR 0x08
  36
  37 /*
  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!
  43  */
  44 #define RNG_TIMEOUT 500
  45
  46 struct stm32_rng_private {
  47         struct hwrng rng;
  48         void __iomem *base;
  49         struct clk *clk;
  50         struct reset_control *rst;
  51 };
  52
  53 static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
  54 {
  55         struct stm32_rng_private *priv =
  56             container_of(rng, struct stm32_rng_private, rng);
  57         u32 sr;
  58         int retval = 0;
  59
  60         pm_runtime_get_sync((struct device *) priv->rng.priv);
  61
  62         while (max > sizeof(u32)) {
  63                 sr = readl_relaxed(priv->base + RNG_SR);
  64                 if (!sr && wait) {
  65                         unsigned int timeout = RNG_TIMEOUT;
  66
  67                         do {
  68                                 cpu_relax();
  69                                 sr = readl_relaxed(priv->base + RNG_SR);
  70                         } while (!sr && --timeout);
  71                 }
  72
  73                 /* If error detected or data not ready... */
  74                 if (sr != RNG_SR_DRDY)
  75                         break;
  76
  77                 *(u32 *)data = readl_relaxed(priv->base + RNG_DR);
  78
  79                 retval += sizeof(u32);
  80                 data += sizeof(u32);
  81                 max -= sizeof(u32);
  82         }
  83
  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);
  87
  88         pm_runtime_mark_last_busy((struct device *) priv->rng.priv);
  89         pm_runtime_put_sync_autosuspend((struct device *) priv->rng.priv);
  90
  91         return retval || !wait ? retval : -EIO;
  92 }
  93
  94 static int stm32_rng_init(struct hwrng *rng)
  95 {
  96         struct stm32_rng_private *priv =
  97             container_of(rng, struct stm32_rng_private, rng);
  98         int err;
  99
 100         err = clk_prepare_enable(priv->clk);
 101         if (err)
 102                 return err;
 103
 104         writel_relaxed(RNG_CR_RNGEN, priv->base + RNG_CR);
 105
 106         /* clear error indicators */
 107         writel_relaxed(0, priv->base + RNG_SR);
 108
 109         return 0;
 110 }
 111
 112 static void stm32_rng_cleanup(struct hwrng *rng)
 113 {
 114         struct stm32_rng_private *priv =
 115             container_of(rng, struct stm32_rng_private, rng);
 116
 117         writel_relaxed(0, priv->base + RNG_CR);
 118         clk_disable_unprepare(priv->clk);
 119 }
 120
 121 static int stm32_rng_probe(struct platform_device *ofdev)
 122 {
 123         struct device *dev = &ofdev->dev;
 124         struct device_node *np = ofdev->dev.of_node;
 125         struct stm32_rng_private *priv;
 126         struct resource res;
 127         int err;
 128
 129         priv = devm_kzalloc(dev, sizeof(struct stm32_rng_private), GFP_KERNEL);
 130         if (!priv)
 131                 return -ENOMEM;
 132
 133         err = of_address_to_resource(np, 0, &res);
 134         if (err)
 135                 return err;
 136
 137         priv->base = devm_ioremap_resource(dev, &res);
 138         if (IS_ERR(priv->base))
 139                 return PTR_ERR(priv->base);
 140
 141         priv->clk = devm_clk_get(&ofdev->dev, NULL);
 142         if (IS_ERR(priv->clk))
 143                 return PTR_ERR(priv->clk);
 144
 145         priv->rst = devm_reset_control_get(&ofdev->dev, NULL);
 146         if (!IS_ERR(priv->rst)) {
 147                 reset_control_assert(priv->rst);
 148                 udelay(2);
 149                 reset_control_deassert(priv->rst);
 150         }
 151
 152         dev_set_drvdata(dev, priv);
 153
 154         priv->rng.name = dev_driver_string(dev),
 155 #ifndef CONFIG_PM
 156         priv->rng.init = stm32_rng_init,
 157         priv->rng.cleanup = stm32_rng_cleanup,
 158 #endif
 159         priv->rng.read = stm32_rng_read,
 160         priv->rng.priv = (unsigned long) dev;
 161
 162         pm_runtime_set_autosuspend_delay(dev, 100);
 163         pm_runtime_use_autosuspend(dev);
 164         pm_runtime_enable(dev);
 165
 166         return devm_hwrng_register(dev, &priv->rng);
 167 }
 168
 169 #ifdef CONFIG_PM
 170 static int stm32_rng_runtime_suspend(struct device *dev)
 171 {
 172         struct stm32_rng_private *priv = dev_get_drvdata(dev);
 173
 174         stm32_rng_cleanup(&priv->rng);
 175
 176         return 0;
 177 }
 178
 179 static int stm32_rng_runtime_resume(struct device *dev)
 180 {
 181         struct stm32_rng_private *priv = dev_get_drvdata(dev);
 182
 183         return stm32_rng_init(&priv->rng);
 184 }
 185 #endif
 186
 187 static UNIVERSAL_DEV_PM_OPS(stm32_rng_pm_ops, stm32_rng_runtime_suspend,
 188                             stm32_rng_runtime_resume, NULL);
 189
 190 static const struct of_device_id stm32_rng_match[] = {
 191         {
 192                 .compatible = "st,stm32-rng",
 193         },
 194         {},
 195 };
 196 MODULE_DEVICE_TABLE(of, stm32_rng_match);
 197
 198 static struct platform_driver stm32_rng_driver = {
 199         .driver = {
 200                 .name = "stm32-rng",
 201                 .pm = &stm32_rng_pm_ops,
 202                 .of_match_table = stm32_rng_match,
 203         },
 204         .probe = stm32_rng_probe,
 205 };
 206
 207 module_platform_driver(stm32_rng_driver);
 208
 209 MODULE_LICENSE("GPL");
 210 MODULE_AUTHOR("Daniel Thompson <daniel.thompson@linaro.org>");
 211 MODULE_DESCRIPTION("STMicroelectronics STM32 RNG device driver");