drivers/char/hw_random/pic32-rng.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * PIC32 RNG driver
   4  *
   5  * Joshua Henderson <[email protected]>
   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/mod_devicetable.h>
  16 #include <linux/module.h>
  17 #include <linux/platform_device.h>
  18 #include <linux/slab.h>
  19
  20 #define RNGCON          0x04
  21 #define TRNGEN          BIT(8)
  22 #define TRNGMOD         BIT(11)
  23 #define RNGSEED1        0x18
  24 #define RNGSEED2        0x1C
  25 #define RNGRCNT         0x20
  26 #define RCNT_MASK       0x7F
  27
  28 struct pic32_rng {
  29         void __iomem    *base;
  30         struct hwrng    rng;
  31 };
  32
  33 /*
  34  * The TRNG can generate up to 24Mbps. This is a timeout that should be safe
  35  * enough given the instructions in the loop and that the TRNG may not always
  36  * be at maximum rate.
  37  */
  38 #define RNG_TIMEOUT 500
  39
  40 static int pic32_rng_init(struct hwrng *rng)
  41 {
  42         struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
  43
  44         /* enable TRNG in enhanced mode */
  45         writel(TRNGEN | TRNGMOD, priv->base + RNGCON);
  46         return 0;
  47 }
  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 void pic32_rng_cleanup(struct hwrng *rng)
  71 {
  72         struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
  73
  74         writel(0, priv->base + RNGCON);
  75 }
  76
  77 static int pic32_rng_probe(struct platform_device *pdev)
  78 {
  79         struct pic32_rng *priv;
  80         struct clk *clk;
  81
  82         priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
  83         if (!priv)
  84                 return -ENOMEM;
  85
  86         priv->base = devm_platform_ioremap_resource(pdev, 0);
  87         if (IS_ERR(priv->base))
  88                 return PTR_ERR(priv->base);
  89
  90         clk = devm_clk_get_enabled(&pdev->dev, NULL);
  91         if (IS_ERR(clk))
  92                 return PTR_ERR(clk);
  93
  94         priv->rng.name = pdev->name;
  95         priv->rng.init = pic32_rng_init;
  96         priv->rng.read = pic32_rng_read;
  97         priv->rng.cleanup = pic32_rng_cleanup;
  98
  99         return devm_hwrng_register(&pdev->dev, &priv->rng);
 100 }
 101
 102 static const struct of_device_id pic32_rng_of_match[] __maybe_unused = {
 103         { .compatible   = "microchip,pic32mzda-rng", },
 104         { /* sentinel */ }
 105 };
 106 MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
 107
 108 static struct platform_driver pic32_rng_driver = {
 109         .probe          = pic32_rng_probe,
 110         .driver         = {
 111                 .name   = "pic32-rng",
 112                 .of_match_table = pic32_rng_of_match,
 113         },
 114 };
 115
 116 module_platform_driver(pic32_rng_driver);
 117
 118 MODULE_LICENSE("GPL");
 119 MODULE_AUTHOR("Joshua Henderson <[email protected]>");
 120 MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");