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/init.h>
  14 #include <linux/device.h>
  15 #include <linux/amba/bus.h>
  16 #include <linux/hw_random.h>
  17 #include <linux/io.h>
  18 #include <linux/clk.h>
  19 #include <linux/err.h>
  20
  21 static struct clk *rng_clk;
  22
  23 static int nmk_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
  24 {
  25         void __iomem *base = (void __iomem *)rng->priv;
  26
  27         /*
  28          * The register is 32 bits and gives 16 random bits (low half).
  29          * A subsequent read will delay the core for 400ns, so we just read
  30          * once and accept the very unlikely very small delay, even if wait==0.
  31          */
  32         *(u16 *)data = __raw_readl(base + 8) & 0xffff;
  33         return 2;
  34 }
  35
  36 /* we have at most one RNG per machine, granted */
  37 static struct hwrng nmk_rng = {
  38         .name           = "nomadik",
  39         .read           = nmk_rng_read,
  40 };
  41
  42 static int nmk_rng_probe(struct amba_device *dev, const struct amba_id *id)
  43 {
  44         void __iomem *base;
  45         int ret;
  46
  47         rng_clk = clk_get(&dev->dev, NULL);
  48         if (IS_ERR(rng_clk)) {
  49                 dev_err(&dev->dev, "could not get rng clock\n");
  50                 ret = PTR_ERR(rng_clk);
  51                 return ret;
  52         }
  53
  54         clk_enable(rng_clk);
  55
  56         ret = amba_request_regions(dev, dev->dev.init_name);
  57         if (ret)
  58                 goto out_clk;
  59         ret = -ENOMEM;
  60         base = ioremap(dev->res.start, 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_unmap;
  67         return 0;
  68
  69 out_unmap:
  70         iounmap(base);
  71 out_release:
  72         amba_release_regions(dev);
  73 out_clk:
  74         clk_disable(rng_clk);
  75         clk_put(rng_clk);
  76         return ret;
  77 }
  78
  79 static int nmk_rng_remove(struct amba_device *dev)
  80 {
  81         void __iomem *base = (void __iomem *)nmk_rng.priv;
  82         hwrng_unregister(&nmk_rng);
  83         iounmap(base);
  84         amba_release_regions(dev);
  85         clk_disable(rng_clk);
  86         clk_put(rng_clk);
  87         return 0;
  88 }
  89
  90 static struct amba_id nmk_rng_ids[] = {
  91         {
  92                 .id     = 0x000805e1,
  93                 .mask   = 0x000fffff, /* top bits are rev and cfg: accept all */
  94         },
  95         {0, 0},
  96 };
  97
  98 MODULE_DEVICE_TABLE(amba, nmk_rng_ids);
  99
 100 static struct amba_driver nmk_rng_driver = {
 101         .drv = {
 102                 .owner = THIS_MODULE,
 103                 .name = "rng",
 104                 },
 105         .probe = nmk_rng_probe,
 106         .remove = nmk_rng_remove,
 107         .id_table = nmk_rng_ids,
 108 };
 109
 110 module_amba_driver(nmk_rng_driver);
 111
 112 MODULE_LICENSE("GPL");