drivers/char/hw_random/nomadik-rng.c

   1 /*
   2  * Nomadik RNG support
   3  *  Copyright 2009 Alessandro Rubini
   4  *
   5  *  This program is free software; you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation; either version 2 of the License, or
   8  *  (at your option) any later version.
   9  */
  10
  11 #include <linux/kernel.h>
  12 #include <linux/module.h>
  13 #include <linux/device.h>
  14 #include <linux/amba/bus.h>
  15 #include <linux/hw_random.h>
  16 #include <linux/io.h>
  17 #include <linux/clk.h>
  18 #include <linux/err.h>
  19
  20 static struct clk *rng_clk;
  21
  22 static int nmk_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
  23 {
  24         void __iomem *base = (void __iomem *)rng->priv;
  25
  26         /*
  27          * The register is 32 bits and gives 16 random bits (low half).
  28          * A subsequent read will delay the core for 400ns, so we just read
  29          * once and accept the very unlikely very small delay, even if wait==0.
  30          */
  31         *(u16 *)data = __raw_readl(base + 8) & 0xffff;
  32         return 2;
  33 }
  34
  35 /* we have at most one RNG per machine, granted */
  36 static struct hwrng nmk_rng = {
  37         .name           = "nomadik",
  38         .read           = nmk_rng_read,
  39 };
  40
  41 static int nmk_rng_probe(struct amba_device *dev, const struct amba_id *id)
  42 {
  43         void __iomem *base;
  44         int ret;
  45
  46         rng_clk = devm_clk_get(&dev->dev, NULL);
  47         if (IS_ERR(rng_clk)) {
  48                 dev_err(&dev->dev, "could not get rng clock\n");
  49                 ret = PTR_ERR(rng_clk);
  50                 return ret;
  51         }
  52
  53         clk_prepare_enable(rng_clk);
  54
  55         ret = amba_request_regions(dev, dev->dev.init_name);
  56         if (ret)
  57                 goto out_clk;
  58         ret = -ENOMEM;
  59         base = devm_ioremap(&dev->dev, dev->res.start,
  60                             resource_size(&dev->res));
  61         if (!base)
  62                 goto out_release;
  63         nmk_rng.priv = (unsigned long)base;
  64         ret = hwrng_register(&nmk_rng);
  65         if (ret)
  66                 goto out_release;
  67         return 0;
  68
  69 out_release:
  70         amba_release_regions(dev);
  71 out_clk:
  72         clk_disable(rng_clk);
  73         return ret;
  74 }
  75
  76 static int nmk_rng_remove(struct amba_device *dev)
  77 {
  78         hwrng_unregister(&nmk_rng);
  79         amba_release_regions(dev);
  80         clk_disable(rng_clk);
  81         return 0;
  82 }
  83
  84 static struct amba_id nmk_rng_ids[] = {
  85         {
  86                 .id     = 0x000805e1,
  87                 .mask   = 0x000fffff, /* top bits are rev and cfg: accept all */
  88         },
  89         {0, 0},
  90 };
  91
  92 MODULE_DEVICE_TABLE(amba, nmk_rng_ids);
  93
  94 static struct amba_driver nmk_rng_driver = {
  95         .drv = {
  96                 .owner = THIS_MODULE,
  97                 .name = "rng",
  98                 },
  99         .probe = nmk_rng_probe,
 100         .remove = nmk_rng_remove,
 101         .id_table = nmk_rng_ids,
 102 };
 103
 104 module_amba_driver(nmk_rng_driver);
 105
 106 MODULE_LICENSE("GPL");