drivers/char/hw_random/pic32-rng.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * PIC32 RNG driver
   4  *
   5  * Joshua Henderson <joshua.henderson@microchip.com>
   6  * Copyright (C) 2016 Microchip Technology Inc.  All rights reserved.
   7  */
   8
   9 #include <linux/clk.h>
  10 #include <linux/clkdev.h>
  11 #include <linux/err.h>
  12 #include <linux/hw_random.h>
  13 #include <linux/io.h>
  14 #include <linux/kernel.h>
  15 #include <linux/module.h>
  16 #include <linux/of.h>
  17 #include <linux/of_device.h>
  18 #include <linux/platform_device.h>
  19 #include <linux/slab.h>
  20
  21 #define RNGCON          0x04
  22 #define  TRNGEN         BIT(8)
  23 #define  PRNGEN         BIT(9)
  24 #define  PRNGCONT       BIT(10)
  25 #define  TRNGMOD        BIT(11)
  26 #define  SEEDLOAD       BIT(12)
  27 #define RNGPOLY1        0x08
  28 #define RNGPOLY2        0x0C
  29 #define RNGNUMGEN1      0x10
  30 #define RNGNUMGEN2      0x14
  31 #define RNGSEED1        0x18
  32 #define RNGSEED2        0x1C
  33 #define RNGRCNT         0x20
  34 #define  RCNT_MASK      0x7F
  35
  36 struct pic32_rng {
  37         void __iomem    *base;
  38         struct hwrng    rng;
  39         struct clk      *clk;
  40 };
  41
  42 /*
  43  * The TRNG can generate up to 24Mbps. This is a timeout that should be safe
  44  * enough given the instructions in the loop and that the TRNG may not always
  45  * be at maximum rate.
  46  */
  47 #define RNG_TIMEOUT 500
  48
  49 static int pic32_rng_read(struct hwrng *rng, void *buf, size_t max,
  50                           bool wait)
  51 {
  52         struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
  53         u64 *data = buf;
  54         u32 t;
  55         unsigned int timeout = RNG_TIMEOUT;
  56
  57         do {
  58                 t = readl(priv->base + RNGRCNT) & RCNT_MASK;
  59                 if (t == 64) {
  60                         /* TRNG value comes through the seed registers */
  61                         *data = ((u64)readl(priv->base + RNGSEED2) << 32) +
  62                                 readl(priv->base + RNGSEED1);
  63                         return 8;
  64                 }
  65         } while (wait && --timeout);
  66
  67         return -EIO;
  68 }
  69
  70 static int pic32_rng_probe(struct platform_device *pdev)
  71 {
  72         struct pic32_rng *priv;
  73         u32 v;
  74         int ret;
  75
  76         priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
  77         if (!priv)
  78                 return -ENOMEM;
  79
  80         priv->base = devm_platform_ioremap_resource(pdev, 0);
  81         if (IS_ERR(priv->base))
  82                 return PTR_ERR(priv->base);
  83
  84         priv->clk = devm_clk_get(&pdev->dev, NULL);
  85         if (IS_ERR(priv->clk))
  86                 return PTR_ERR(priv->clk);
  87
  88         ret = clk_prepare_enable(priv->clk);
  89         if (ret)
  90                 return ret;
  91
  92         /* enable TRNG in enhanced mode */
  93         v = TRNGEN | TRNGMOD;
  94         writel(v, priv->base + RNGCON);
  95
  96         priv->rng.name = pdev->name;
  97         priv->rng.read = pic32_rng_read;
  98
  99         ret = hwrng_register(&priv->rng);
 100         if (ret)
 101                 goto err_register;
 102
 103         platform_set_drvdata(pdev, priv);
 104
 105         return 0;
 106
 107 err_register:
 108         clk_disable_unprepare(priv->clk);
 109         return ret;
 110 }
 111
 112 static int pic32_rng_remove(struct platform_device *pdev)
 113 {
 114         struct pic32_rng *rng = platform_get_drvdata(pdev);
 115
 116         hwrng_unregister(&rng->rng);
 117         writel(0, rng->base + RNGCON);
 118         clk_disable_unprepare(rng->clk);
 119         return 0;
 120 }
 121
 122 static const struct of_device_id pic32_rng_of_match[] = {
 123         { .compatible   = "microchip,pic32mzda-rng", },
 124         { /* sentinel */ }
 125 };
 126 MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
 127
 128 static struct platform_driver pic32_rng_driver = {
 129         .probe          = pic32_rng_probe,
 130         .remove         = pic32_rng_remove,
 131         .driver         = {
 132                 .name   = "pic32-rng",
 133                 .of_match_table = of_match_ptr(pic32_rng_of_match),
 134         },
 135 };
 136
 137 module_platform_driver(pic32_rng_driver);
 138
 139 MODULE_LICENSE("GPL");
 140 MODULE_AUTHOR("Joshua Henderson <joshua.henderson@microchip.com>");
 141 MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");