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         do {
  66                 t = readl(priv->base + RNGRCNT) & RCNT_MASK;
  67                 if (t == 64) {
  68                         /* TRNG value comes through the seed registers */
  69                         *data = ((u64)readl(priv->base + RNGSEED2) << 32) +
  70                                 readl(priv->base + RNGSEED1);
  71                         return 8;
  72                 }
  73         } while (wait && --timeout);
  74
  75         return -EIO;
  76 }
  77
  78 static int pic32_rng_probe(struct platform_device *pdev)
  79 {
  80         struct pic32_rng *priv;
  81         struct resource *res;
  82         u32 v;
  83         int ret;
  84
  85         priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
  86         if (!priv)
  87                 return -ENOMEM;
  88
  89         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  90         priv->base = devm_ioremap_resource(&pdev->dev, res);
  91         if (IS_ERR(priv->base))
  92                 return PTR_ERR(priv->base);
  93
  94         priv->clk = devm_clk_get(&pdev->dev, NULL);
  95         if (IS_ERR(priv->clk))
  96                 return PTR_ERR(priv->clk);
  97
  98         ret = clk_prepare_enable(priv->clk);
  99         if (ret)
 100                 return ret;
 101
 102         /* enable TRNG in enhanced mode */
 103         v = TRNGEN | TRNGMOD;
 104         writel(v, priv->base + RNGCON);
 105
 106         priv->rng.name = pdev->name;
 107         priv->rng.read = pic32_rng_read;
 108
 109         ret = hwrng_register(&priv->rng);
 110         if (ret)
 111                 goto err_register;
 112
 113         platform_set_drvdata(pdev, priv);
 114
 115         return 0;
 116
 117 err_register:
 118         clk_disable_unprepare(priv->clk);
 119         return ret;
 120 }
 121
 122 static int pic32_rng_remove(struct platform_device *pdev)
 123 {
 124         struct pic32_rng *rng = platform_get_drvdata(pdev);
 125
 126         hwrng_unregister(&rng->rng);
 127         writel(0, rng->base + RNGCON);
 128         clk_disable_unprepare(rng->clk);
 129         return 0;
 130 }
 131
 132 static const struct of_device_id pic32_rng_of_match[] = {
 133         { .compatible   = "microchip,pic32mzda-rng", },
 134         { /* sentinel */ }
 135 };
 136 MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
 137
 138 static struct platform_driver pic32_rng_driver = {
 139         .probe          = pic32_rng_probe,
 140         .remove         = pic32_rng_remove,
 141         .driver         = {
 142                 .name   = "pic32-rng",
 143                 .of_match_table = of_match_ptr(pic32_rng_of_match),
 144         },
 145 };
 146
 147 module_platform_driver(pic32_rng_driver);
 148
 149 MODULE_LICENSE("GPL");
 150 MODULE_AUTHOR("Joshua Henderson <joshua.henderson@microchip.com>");
 151 MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");