drivers/char/hw_random/pic32-rng.c

   1 /*
   2  * PIC32 RNG driver
   3  *
   4  * Joshua Henderson <joshua.henderson@microchip.com>
   5  * Copyright (C) 2016 Microchip Technology Inc.  All rights reserved.
   6  *
   7  * This program is free software; you can distribute it and/or modify it
   8  * under the terms of the GNU General Public License (Version 2) as
   9  * published by the Free Software Foundation.
  10  *
  11  * This program is distributed in the hope it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * for more details.
  15  */
  16
  17 #include <linux/clk.h>
  18 #include <linux/clkdev.h>
  19 #include <linux/err.h>
  20 #include <linux/hw_random.h>
  21 #include <linux/io.h>
  22 #include <linux/kernel.h>
  23 #include <linux/module.h>
  24 #include <linux/of.h>
  25 #include <linux/of_device.h>
  26 #include <linux/platform_device.h>
  27 #include <linux/slab.h>
  28
  29 #define RNGCON          0x04
  30 #define  TRNGEN         BIT(8)
  31 #define  PRNGEN         BIT(9)
  32 #define  PRNGCONT       BIT(10)
  33 #define  TRNGMOD        BIT(11)
  34 #define  SEEDLOAD       BIT(12)
  35 #define RNGPOLY1        0x08
  36 #define RNGPOLY2        0x0C
  37 #define RNGNUMGEN1      0x10
  38 #define RNGNUMGEN2      0x14
  39 #define RNGSEED1        0x18
  40 #define RNGSEED2        0x1C
  41 #define RNGRCNT         0x20
  42 #define  RCNT_MASK      0x7F
  43
  44 struct pic32_rng {
  45         void __iomem    *base;
  46         struct hwrng    rng;
  47         struct clk      *clk;
  48 };
  49
  50 /*
  51  * The TRNG can generate up to 24Mbps. This is a timeout that should be safe
  52  * enough given the instructions in the loop and that the TRNG may not always
  53  * be at maximum rate.
  54  */
  55 #define RNG_TIMEOUT 500
  56
  57 static int pic32_rng_read(struct hwrng *rng, void *buf, size_t max,
  58                           bool wait)
  59 {
  60         struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
  61         u64 *data = buf;
  62         u32 t;
  63         unsigned int timeout = RNG_TIMEOUT;
  64
  65         if (max < 8)
  66                 return 0;
  67
  68         do {
  69                 t = readl(priv->base + RNGRCNT) & RCNT_MASK;
  70                 if (t == 64) {
  71                         /* TRNG value comes through the seed registers */
  72                         *data = ((u64)readl(priv->base + RNGSEED2) << 32) +
  73                                 readl(priv->base + RNGSEED1);
  74                         return 8;
  75                 }
  76         } while (wait && --timeout);
  77
  78         return -EIO;
  79 }
  80
  81 static int pic32_rng_probe(struct platform_device *pdev)
  82 {
  83         struct pic32_rng *priv;
  84         struct resource *res;
  85         u32 v;
  86         int ret;
  87
  88         priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
  89         if (!priv)
  90                 return -ENOMEM;
  91
  92         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  93         priv->base = devm_ioremap_resource(&pdev->dev, res);
  94         if (IS_ERR(priv->base))
  95                 return PTR_ERR(priv->base);
  96
  97         priv->clk = devm_clk_get(&pdev->dev, NULL);
  98         if (IS_ERR(priv->clk))
  99                 return PTR_ERR(priv->clk);
 100
 101         ret = clk_prepare_enable(priv->clk);
 102         if (ret)
 103                 return ret;
 104
 105         /* enable TRNG in enhanced mode */
 106         v = TRNGEN | TRNGMOD;
 107         writel(v, priv->base + RNGCON);
 108
 109         priv->rng.name = pdev->name;
 110         priv->rng.read = pic32_rng_read;
 111
 112         ret = hwrng_register(&priv->rng);
 113         if (ret)
 114                 goto err_register;
 115
 116         platform_set_drvdata(pdev, priv);
 117
 118         return 0;
 119
 120 err_register:
 121         clk_disable_unprepare(priv->clk);
 122         return ret;
 123 }
 124
 125 static int pic32_rng_remove(struct platform_device *pdev)
 126 {
 127         struct pic32_rng *rng = platform_get_drvdata(pdev);
 128
 129         hwrng_unregister(&rng->rng);
 130         writel(0, rng->base + RNGCON);
 131         clk_disable_unprepare(rng->clk);
 132         return 0;
 133 }
 134
 135 static const struct of_device_id pic32_rng_of_match[] = {
 136         { .compatible   = "microchip,pic32mzda-rng", },
 137         { /* sentinel */ }
 138 };
 139 MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
 140
 141 static struct platform_driver pic32_rng_driver = {
 142         .probe          = pic32_rng_probe,
 143         .remove         = pic32_rng_remove,
 144         .driver         = {
 145                 .name   = "pic32-rng",
 146                 .owner  = THIS_MODULE,
 147                 .of_match_table = of_match_ptr(pic32_rng_of_match),
 148         },
 149 };
 150
 151 module_platform_driver(pic32_rng_driver);
 152
 153 MODULE_LICENSE("GPL");
 154 MODULE_AUTHOR("Joshua Henderson <joshua.henderson@microchip.com>");
 155 MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");