drivers/char/hw_random/bcm74110-rng.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (c) 2024 Broadcom
   4  */
   5
   6 #define pr_fmt(fmt)     KBUILD_MODNAME ": " fmt
   7
   8 #include <linux/module.h>
   9 #include <linux/mod_devicetable.h>
  10 #include <linux/kernel.h>
  11 #include <linux/io.h>
  12 #include <linux/delay.h>
  13 #include <linux/platform_device.h>
  14 #include <linux/random.h>
  15 #include <linux/hw_random.h>
  16
  17 #define HOST_REV_ID             0x00
  18 #define HOST_FIFO_DEPTH         0x04
  19 #define HOST_FIFO_COUNT         0x08
  20 #define HOST_FIFO_THRESHOLD     0x0c
  21 #define HOST_FIFO_DATA          0x10
  22
  23 #define HOST_FIFO_COUNT_MASK            0xffff
  24
  25 /* Delay range in microseconds */
  26 #define FIFO_DELAY_MIN_US               3
  27 #define FIFO_DELAY_MAX_US               7
  28 #define FIFO_DELAY_MAX_COUNT            10
  29
  30 struct bcm74110_priv {
  31         void __iomem *base;
  32 };
  33
  34 static inline int bcm74110_rng_fifo_count(void __iomem *mem)
  35 {
  36         return readl_relaxed(mem) & HOST_FIFO_COUNT_MASK;
  37 }
  38
  39 static int bcm74110_rng_read(struct hwrng *rng, void *buf, size_t max,
  40                         bool wait)
  41 {
  42         struct bcm74110_priv *priv = (struct bcm74110_priv *)rng->priv;
  43         void __iomem *fc_addr = priv->base + HOST_FIFO_COUNT;
  44         void __iomem *fd_addr = priv->base + HOST_FIFO_DATA;
  45         unsigned underrun_count = 0;
  46         u32 max_words = max / sizeof(u32);
  47         u32 num_words;
  48         unsigned i;
  49
  50         /*
  51          * We need to check how many words are available in the RNG FIFO. If
  52          * there aren't any, we need to wait for some to become available.
  53          */
  54         while ((num_words = bcm74110_rng_fifo_count(fc_addr)) == 0) {
  55                 if (!wait)
  56                         return 0;
  57                 /*
  58                  * As a precaution, limit how long we wait. If the FIFO doesn't
  59                  * refill within the allotted time, return 0 (=no data) to the
  60                  * caller.
  61                  */
  62                 if (likely(underrun_count < FIFO_DELAY_MAX_COUNT))
  63                         usleep_range(FIFO_DELAY_MIN_US, FIFO_DELAY_MAX_US);
  64                 else
  65                         return 0;
  66                 underrun_count++;
  67         }
  68         if (num_words > max_words)
  69                 num_words = max_words;
  70
  71         /* Bail early if we run out of random numbers unexpectedly */
  72         for (i = 0; i < num_words && bcm74110_rng_fifo_count(fc_addr) > 0; i++)
  73                 ((u32 *)buf)[i] = readl_relaxed(fd_addr);
  74
  75         return i * sizeof(u32);
  76 }
  77
  78 static struct hwrng bcm74110_hwrng = {
  79         .read = bcm74110_rng_read,
  80 };
  81
  82 static int bcm74110_rng_probe(struct platform_device *pdev)
  83 {
  84         struct device *dev = &pdev->dev;
  85         struct bcm74110_priv *priv;
  86         int rc;
  87
  88         priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
  89         if (!priv)
  90                 return -ENOMEM;
  91
  92         bcm74110_hwrng.name = pdev->name;
  93         bcm74110_hwrng.priv = (unsigned long)priv;
  94
  95         priv->base = devm_platform_ioremap_resource(pdev, 0);
  96         if (IS_ERR(priv->base))
  97                 return PTR_ERR(priv->base);
  98
  99         rc = devm_hwrng_register(dev, &bcm74110_hwrng);
 100         if (rc)
 101                 dev_err(dev, "hwrng registration failed (%d)\n", rc);
 102         else
 103                 dev_info(dev, "hwrng registered\n");
 104
 105         return rc;
 106 }
 107
 108 static const struct of_device_id bcm74110_rng_match[] = {
 109         { .compatible   = "brcm,bcm74110-rng", },
 110         {},
 111 };
 112 MODULE_DEVICE_TABLE(of, bcm74110_rng_match);
 113
 114 static struct platform_driver bcm74110_rng_driver = {
 115         .driver = {
 116                 .name = KBUILD_MODNAME,
 117                 .of_match_table = bcm74110_rng_match,
 118         },
 119         .probe  = bcm74110_rng_probe,
 120 };
 121 module_platform_driver(bcm74110_rng_driver);
 122
 123 MODULE_AUTHOR("Markus Mayer <mmayer@broadcom.com>");
 124 MODULE_DESCRIPTION("BCM 74110 Random Number Generator (RNG) driver");
 125 MODULE_LICENSE("GPL v2");