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/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");